Stone Mountain is an exposed
granitic pluton, located in Northeast Georgia. Uniformitarian estimates
suggest that the granite was intruded into overlying metamorphic rocks
during the last stages of the Alleghenian Orogeny. Later the mountain
became exposed at the earth's surface. The uniformitarian model for
the formation of Stone Mountain remains unresolved. This paper presents
an interpretation, using the young earth Flood model, for the origin
of Stone Mountain which would predict its formation and exposure during
the Flood event.
The Appalachian Mountains
form a belt stretching from northeast Alabama to Newfoundland. The mountains
are usually separated into northern and southern arcs. It has been proposed
that the Southern Appalachian mountain arc has undergone several orogenic
events resulting in the complicated folding and faulting of the associated
rocks (Cook, Brown and Oliver, 1980, pp. 152- 153;
Dallmeyer, 1978, p. 124;
Windley, 1977, pp. 183-192). The core of the Southern Appalachian Inner
Piedmont is composed of a high-grade migmatitic assemblage of biotite
gneiss, granites and granitic gneiss, and minor but widespread amphibolite
(Dallmeyer, 1978, p. 127). The Inner Piedmont granitic rock types are
associated with an intrusive magma, a molten rock generated deep within
the earth's crust. The molten granite rises toward the earth's surface
but fails to erupt due to a variety of causes (e.g., heat loss, orogenic
activity ends, loss of fluids, etc.). The magma then cooled in the subsurface
and solidified into large masses of intrusive granitic rock, called
Stone Mountain is one such
pluton and it is exposed at the earth's surface. The current uniformitarian
model for the emplacement and exposure of Stone Mountain remains in
question. The uniformitarian model will be presented to the reader in
an effort to show how some of these data can be used to support the
young earth Flood modeler in reconstructing events in earth's past relating
to the formation and exposure of Stone Mountain. Specifically, this
paper will discuss the formation of Stone Mountain within the context
of the Flood model, which this author believes offers a better model
for the emplacement and exposure of Stone Mountain. Age dates used in
this paper will reflect those presented within the uniformitarian literature.
However, the author does not accept the uniformitarian assumptions or
dates as presented and will suggest a chronology within the young earth
Flood model. A glossary of terms is provided to aid the reader in understanding
some of the geologic terminology used in this article.
Stone Mountain is one of
many granitic plutons exposed in Georgia (Figure 1). Stone Mountain,
located approximately 16 miles east of Atlanta, Georgia, rises approximately
780 feet above the generally flat to slightly rolling land surface,
forming a geomorphic feature called a monadnock (Figure 2). The mountain
is observable from tens of miles away and is surrounded, at ground level,
by metamorphic rocks and "Stone Mountain Granite." The highest
point of the mountain is 1683 feet above sea-level. Questions remain
as to how much overlying rock (termed overburden) once covered the mountain.
The overburden thickness has been estimated as 2 to 10 miles (Anonymous,
1987; Grant, 1986, p. 285; Whitney, Jones and Walker, 1976, p. 1067;
Atkins and Joyce, 1980, p. 1). The removal of the overburden is a very
important point in the reconstruction for the exposure of Stone Mountain.
It is proposed to have been removed through slow uniformitarian weathering
processes and uplift. These points are key points of separation between
the two models. The important thing to remember in considering the amount
of overburden is the fact that it is now gone!
The original sediments which,
through heat and pressure, altered into a granitic magma, and which
now form Stone Mountain are believed to have been derived from clastic
(i.e., sandy to argillaceous) sediments possibly combined with volcanic
flows or ash deposits (Grant, 1962, p. 5; Hermann, 1954, p. 78-79).
Tectonic and orogenic events associated with the formation of the Southern
Appalachians resulted in the transformation of the original clastics
into metamorphic rocks. The formation of the metamorphic rocks, which
account for much of what is believed to have been overburden, date to
Precambrian time (Herrmann, 1954, p. XV).
Stone Mountain is believed
to have been intruded in the last orogenic event (Alleghenian Orogeny)
associated with the Southern Appalachians. For a suggested uniformitarian
chronology of events associated with the formation of Stone Mountain,
see Appendix I.
According to Whitney et
al. (1976, p. 1073), the Stone Mountain Granite was intruded into the
Lithonia Gneiss and the overlying metamorphic rocks during the Late
Pennsylvanian Period. This age date correlates directly with a belt
of intrusives in South and North Carolina identified as the "300
Ma old group" (Fullagar, 1971, pp. 2856-2857; McSween, Speer and
Fullagar, 1991, pp. 121-125).
Stone Mountain Granite may
represent an anatectic granite which was possibly derived from the surrounding
metamorphic rock. However, serious questions remain and the source rock
for the Stone Mountain pluton and surrounding granitic rock mass remains
an unresolved mystery (Grant et al., 1980, p. 52).
Flow structures developed
during the intrusion of the pluton which include flowage foliation,
mica fluctuation about an axis of rotation, and parallel orientation
of micaceous autoliths (Herrmann, 1954, p. XV). These flow structures
are also believed to show that the mountain was not intruded in one
event, but rather in several pulses, reflected by the occurrence of
flow- banded autoliths which represent an earlier cooling period [Figure
3] (Grant 1962, p. 6; Grant et al., 1980, p. 47; Grant 1986, p. 286).
According to Grant et al.
(1980, p. 48), the magma intruded from the east into previously folded
metamorphic rocks, as indicated by fold structures. However, it is also
possible that the granite was intruded upward through northwest trending
dikes (Grant, 1986, p. 286). The intrusion possibly started with the
formation of a small, probably basally flattened ellipsoidal mass of
magma (Grant et al., 1980, p. 48). The magma expanded parting the country
rock into thin sheets. With further intrusion and expansion the country
rock would be broken into xenoliths (Figure 4), which were carried outward
and away from the initial point of intrusion (Grant et al., 1980, p.
48). The magma is believed to have cooled from west to east as indicated
by mica growth in xenoliths found on the east end of the mountain, but
not on the west end.
Questions remain regarding
the rates of both uplift and erosion. An evaluation of the data shows
confusing emplacement depths and uplift and erosional rates. For example,
uplift is believed to have played a role in the exposure of Stone Mountain.
Erosion alone could only have removed 6 to 8 km (3.7 to 5 miles) of
overburden (Dallmeyer, 1978, pp. 142-143; Whitney et al., 1976, p. 1076).
The remaining 10 to 15 km (6.2 to 9.3 miles) of overburden is believed
to have been removed by subsequent uplift, but this remains unproven.
These numbers do not add up and this reflects just one point of weakness
in the uniformitarian model for the formation of Stone Mountain.
As previously mentioned,
the rate of uplift remains unresolved. According to Dallmeyer (1978,
p. 142 ), the Stone Mountain pluton was uplifted 37,729 feet (7.1 miles)
over 71 Ma. Debate exists as to when Stone Mountain became exposed at
earth's surface. Dallmeyer (1978, pp. 141-143) has proposed that Stone
Mountain became exposed around 220 Ma ago and offers the Late Triassic
unconformity between the crystalline rocks and nonmarine clastic rock
within the Dan River Basin of North Carolina as evidence. Atkins and
Joyce (1980, p. 1) suggest that the mountain became exposed only 15
Stone Mountain, a leucocratic
adamellite or quartz monzonite (Hermann, 1958, p. 29; Whitney et al.,
1976, p. 1067), ranges in compositional variation between a granite
(nearly equal amounts of quartz, alkali feldspar and plagioclase) to
granodiorite (containing equal amounts of quartz and plagioclase with
10% to 25% alkali feldspar) [Grant, Size and O'Connor, 1980, p. 43].
Two divergent opinions exist
for the formation of Stone Mountain Granite. According to Whitney et
al. (1976, p. 1071), in terms of mineralogy and major and minor-element
chemistry, Stone Mountain Granite has a highly differentiated composition
brought about by fractional crystallization and fractional melting.
This has resulted in a granite of homogenous peraluminous composition,
lacking chemically related mafic lithologies. However, according to
Grant et al. (1980, p. 44), the wide range in silica composition for
the Stone Mountain Granite is believed to represent repeated periods
of anatectic granite-melt emplacement rather than indicating a trend
in magma differentiation. These conflicting models for the granitic
magma source reveal to the reader that serious questions remain regarding
a suitable source material.
The minerals which compose
the Stone Mountain Granite are described as fine to medium-grained.
The granite is composed of quartz, plagioclase feldspar, microcline
and muscovite with a minor amount of brown biotite and small tourmaline
clusters (Herrmann, 1954, p. 30; Grant et al., 1980, p. 43). The grain
size of those minerals, which compose the granitic rock, is believed
to be a function of the amount of time that magma has to cool. The faster
that magma cools the smaller the grain size of the minerals which form.
Stone Mountain granitic rock mineral grain size ranges from 1 to 4 mm
(Grant et al., 1980, p. 43). An interesting feature of Stone mountain
Granite is that the grain size is equigranular across the entire mountain.
This suggests that the mountain cooling quickly and uniformly. Additionally,
the granite exhibits flow banding at several areas across the mountain
(Grant, 1986, p. 287). This implies that as the magma was flowing as
it was cooling and forming minerals. This movement would serve to expose
greater surface area to cooling by the surrounding country rock. Yet
with cooling occurring across the granitic mass, the granite retained
its uniform granular size and composition.
Xenoliths are chunks of
the original country rock in the granitic rock. The xenoliths found
at Stone Mountain consist of biotite gneiss and amphibolite which are
believed to be characteristic of the older metamorphic rocks which at
one time covered the mountain [Figure 4] (Atkins and Joyce, 1980, p.
11). The lithology of the xenoliths varies and includes biotite and
a muscovite-biotite with garnet mica schist (Grant et al., 1980, p.
47). Distribution of the xenoliths is irregular, with concentrations
predominantly on the east and west ends of the mountain. Structures
in xenoliths include schistosity and gneissic banding (Grant et al.,
1980, p. 47).
Sheeting structure is displayed
over the entire surface of Stone Mountain. Individual sheets range from
a fraction of an inch up to several feet or possibly even tens of feet
in thickness (Hopson, 1958, p. 65). Sheet formation has been attributed
to the release of overburden confining pressure, which has resulted
in the expansion (dilation) of the granitic rock. Dale (1923, p. 30)
found that newly quarried blocks of Stone Mountain granite expanded
0.1 percent in the direction of greatest confinement. Hopson (1958,
p. 65) has reported sheets of Stone Mountain granite as thick as 12
feet. Sheet thickness has been found to increase with depth. The sheeting
of the Stone Mountain Granite will vary due to uplift, warping, release
of confining overburden, etc., and will contribute to the breakup and
erosion of the mountain.
Jointing on Stone Mountain
is generally poorly developed. Joint attitude measurements collected
from different areas of the mountain show no preferential orientation
for development [Figure 5] (Grant et al., 1980, p. 47). Joints and joint
sets are believed to be caused by two different mechanisms. The first
is due to stress during folding and the second is due to contraction
of the cooling magma (Atkins and Joyce, 1980, p. 5). Some joints remain
as unfilled cracks in the rock, while other joints have been filled
with magma intruded later, forming dikes. The mineral composition of
the dike is believed to reflect the rate at which they cooled. Aplite
dikes form where fast cooling conditions existed (smaller rock crystal
sizes), while pegmatite dikes (Figure 6) formed under more slow cooling
conditions (larger rock crystal sizes). Additionally, a third type of
dike exists at Stone Mountain. These dikes show no real zone of contact,
rather these dikes blend into the surrounding granitic rock (Figure
7). These blended contacts suggest that the dike was intruded into the
granite while the granite was still molten (Lahee, 1931, pp. 128-129).
Also associated with the jointing are biotite schlieren, which appear
to be the result of sheared xenoliths rather than magmatically formed
concentrations of biotite (Figure 8). Both Mount Arabia, a migmatite
dome to the south, and Stone Mountain show minor, late brittle faulting
and mineralization along joints which is believed to be in association
with intrusion of Triassic diabase dikes (Grant, et al., 1980, p. 41).
Much like what was previously stated regarding sheeting, the jointing,
fracturing and faulting will occur at various rates due to uplift, warping,
breaking of granitic sheets, release of confining overburden, etc.,
and will contribute to the erosion to the mountain.
Fractures are created by
both physical (e.g. dilation, expansion and contraction due to temperature
changes, freezing and thawing of the water within the fractures and
exfoliation) and chemical (rainwater and plant acid dissolution of the
minerals) processes (Figure 9). Fractures also serve as conduits for
water movement and several areas of the park have natural flowing springs
immediately following precipitation events (Figure 10).
Sometime following the intrusion
or intrusions of the granitic pluton into the surrounding country rock,
another intrusive event occurred quite different from the previous ones.
This intrusion was composed of diabase, a rock of basaltic composition
(Figure 11). It is unknown whether this rock was derived from melted
crustal rock or from deeper rock derived from the earth's mantle. The
diabase dikes appear to trend in a northwest - southeast direction (Atkins
and Joyce, 1980, pp. 12 - 13). These diabase dikes are associated with
a Triassic age rift which occurred along the eastern side of the Appalachian
mountains and are believed to have formed as a result of the breakup
of the Pangaean supercontinent (Olsen, Froelich, Daniels, Smoot, and
Gore, 1991, p. 142). A chronological reconstruction of the intrusive
events associated with dikes is given in Appendix II.
Today the surface of the
mountain is exposed to atmospheric erosional processes. Weathering begins
with meteoric water percolating downward through vertical joints of
tectonic origin and horizontally along sheet joints which are of dilation
origin (Grant, 1963, p. 70). The jointing and fracturing aids in the
exfoliation (thin sheets of rock which break off parallel to the surface
of the exposed rock - like the skin of an onion) process of erosion,
by breaking the rocks into blocks (Figure 12). Weathering enhances the
exfoliation of the rock resulting in some cases, in the complete detachment
of the block from the mountain (Figure 13). This exfoliation process
was exploited by quarry workers when the Mountain was a source of granite
(Figure 14). Stone Mountain is now a Confederate Memorial Park and is
no longer quarried for granite.
Today the mountain continues
to exfoliate layers of granite from its surface (Figure 15). Additionally,
many spall layers lie at the base of the mountain and reflect the fact
that they were at one time a part of the mountain (Figure 16). Exfoliation
is likely the greatest single process controlling the dome shape of
Stone Mountain (Grant et al., 1980, p. 43; Hopson, 1958, p.73).
A weathering pattern particularly
associated with the granite pavement is the pit and dome structure [Figure
17] (Grant, 1986, pp. 286-287). Domes form as areas around them erode
into pits. They are believed to be formed by dilation and associated
weathering (Grant, 1986, p. 285). The pits or depressions fill with
water following precipitation events, turning them into vernal pools
(Figure 18). Lammerts (1978) discusses the unique flora and fauna associated
with vernal pools occurring in the western U.S. and their possible time
of formation within the context of the Flood model. The vernal pools
at Stone Mountain range in size from 6 inches to a few tens of feet
in diameter and are also home to unique (but surprisingly similar to
those discussed by Lammerts) forms of plant and animal life. Two different
types of shrimp (i.e., clam and fairy) live in the clear freshwater
pools during the rainy season (Anonymous, 1987). Smith (1941, pp. 117-127)
found that the standing water in the depressions were acidic (pH 5.0
- 5.4) due to plant activity. He further speculated that the acids contributed
to the chemical weathering of the granite. Additionally, it is now recognized
that acid rain exists, due to air pollution, at a pH around the previously
stated range and also contributes to the chemical weathering of the
A second type of weathering
pit has developed on Stone Mountain. These pits are small, elliptically
shaped depressions which aligned parallel to the flow structure of the
granite [Figure 19] (Herrmann, 1954, p. 6; Hopson, 1958, pp. 72-73).
This author believes that these secondary elliptical pits also weather
to form vernal pools seen on the mountain.
Rocks exposed at the top
of the mountain are subject to freezing and thawing (winter months)
and heating and cooling (summer months). The freezing and thawing weathering
process is believed to have created a weathering pattern similar to
what is seen on the Antarctic continent (Figure 20). Differential erosion
occurs where there is a variation in rock composition. This has occurred
where the granite has weathered away around the harder tourmaline crystals,
creating a pimple like surface (Figure 21). Additionally, wind blown
sand contributes in a minor way to the erosion of the mountain by abrasion.
According to Hopson (1958,
pp. 75-79), intergranular wedging by crystallizing salts and expansion
of mineral grains accompanying hydration are probably the two most effective
weathering mechanisms working to break down the granite. According to
Hopson (1958, pp. 75-79), Stone Mountain granite is no longer considered
of sufficient grade or quality for use as monumental stone due to its
low resistance to weathering. The granite has been shown to weather
rapidly in a moist environment. The granite weathers into sheets and/or
blocks, which further weathers to form a saprolite (i.e., soil).
Saprolite develops as a
result of weathering of the granitic or basaltic rock. Weathering of
the granite produces a saprolite composed predominately of kaolinite,
with minor amounts of endellite, quartz, muscovite and microcline (Grant,
1963, p. 70). The saprolite is usually white and structureless, containing
disseminated muscovite flakes [Figure 22] (Herrmann, 1954, p. 5). Where
diabase dikes (i.e., basalt) are present the saprolite develops a deep
red color, due to the iron content of diabase, which oxides.
The relatively thin layer
of saprolite overburden on and around Stone Mountain (ranging from 0
to 8 feet) reflect, in the author's opinion, the short amount of time
that has been available for soil to develop. The author believes that
greater saprolite development should have occurred if the 15 Ma exposure
time is used, and especially if the 220 Ma date is correct.
On the mountain pavement,
the eroded sand size particles accumulate in areas of low relief behind
large objects which block the wind (Figure 23). With a sufficient buildup
of this soil, plant life is able to establish itself and grow (Figure
24). Due to the increase in organic content in the soil, the white saprolite
changes to a gray and/or black color (Herrmann, 1954, p. 5). Studies
of the soils show an increase in clay mineral content with soil thickness
(Grant, 1986, p. 287).
The author supports Gentry's
(1988, p. 133; pp. 184-185) position regarding the formation of granites
during the creation week (e.g., granite cores of the proto-Southern
Appalachians) and again during the Flood event (e.g. Stone Mountain
Granite). From a creation geologist's perspective the Appalachian mountains
might have had their beginnings when land was first separated from the
waters during the creation week (Genesis 1:9). Uniformitarian geoscientists
have classified the Appalachian granites in Georgia into either older
or younger intrusives, with the Stone Mountain Granite falling into
the younger category (Crickmay, 1952, p. 34). It is further believed
that Stone Mountain was intruded at or near the end of the regional
deformation (Alleghenian Orogeny) associated with the Southern Appalachians
(Grant, 1962, p. 6; Grant et al., 1980, p. 41).
According to McQueen (1987,
p. 247), the orogenic activity associated with the formation of the
Appalachian mountains took place over a six month timeframe towards
the end of the Flood event; he defines this time interval as Phase III.
McQueen did not differentiate between the uniformitarian orogenic events
associated with the deformation of the Southern Appalachian mountains
(i.e., Late Precambrian/Cambrian, Taconic, Acadian and Alleghenian orogenies).
The author believes that one or more of the above referenced orogenies
could be associated with the Creation week and the remaining orogenies
could be associated with the Flood event. According to Whitcomb and
Morris (1961, p. 8), the Flood waters began to recede beginning on the
150'th day. The decrease in water level could directly relate to tectonism
via seafloor spreading, continental collisions and tensional lateral
plate movements. The author supports McQueen's position for the formation
of the Stone Mountain pluton towards the end of the Alleghenian Orogeny
(defined by this author as a late Flood orogenic event) in association
with the latter stages of the Flood event. Additionally, this author
believes that the Stone Mountain granitic magma formed as a result of
the mixing of some remelted original primordial granite with melted
surrounding rocks and sediments (Gentry, 1988, pp. 184-185). This could
explain why the Stone Mountain Granite is compositionally different
from all of the other granites in the area.
The author suggests that
possibly the source magma of Stone Mountain was derived from deep within
the crust during the tectonic event identified as the Alleghenian Orogeny
(a Flood generated orogenic event). Tremendous heat and pressure were
generated during this event and the author believes that two separate
magmas were created, one being the crustal felsic or granitic magma
(of which Stone Mountain is composed) and the other being the mantle
mafic or basaltic magma (of which the basalt dikes are composed). Initially
the lighter and larger felsic magma would rise quickly being intruded
into the metamorphic overburden. The smaller slower rising mafic magma
would be later intruded into the cooling semi-solid granitic rock mass
and any metamorphic country rock not eroded by Flood waters, thus providing
both granitic rock and basaltic dikes. Support for my suggestion comes
from the fact that the Southern Appalachian Mountains and all of the
orogenic events associated with their formation are viewed (by uniformitarian
research) as having occurred as a result of stacking and shuffling of
relatively thin sheets of crustal material and all basaltic rock is
viewed as being derived from the earth's mantle (Cook et al., 1980,
pp. 139-155). The diabase intrusions into the Stone Mountain Granite
are believed to have occurred during a rifting period in the Triassic
(also a Flood generated orogenic event). Additional research and field
work is necessary to reconstruct how this event occurred and the diabase
The formation of granitic
rock remains a mystery for geologists. Gentry (1988, p. 131) has pointed
out that with all of the volcanic activity across the earth, geologists
have yet to show how granites crystallize from a granite melt. Even
today there is no way of recreating in the laboratory how granite forms
in the subsurface. So the question of how and why granites form coarse
grained structures as opposed to fine grained structures remains an
Granitic rock is commonly
characterized by grain size and composition and the Stone Mountain Granite
is no exception. What is interesting is the fact that Stone Mountain
Granite is the same, both in grain size and mineral composition, from
the east end to the west end of the mountain (a distance of approximately
1.8 miles). Normally magmatic masses are said to cool over millions
of years and vary in composition due to differentiation of the cooling
magma. Stone Mountain does not show any differentiation in granitic
composition. The author believes that the homogeneity of the granite
reflects rapid emplacement. At a later time additional intrusive events
occurred resulting in pegmatite and aplite dikes and later still the
diabase dikes which cross-cut the granite.
The amount of time suggested
by the previously cited authors for the cooling and exposure of the
Stone Mountain granite (i.e., 71 Ma) is quite rapid considering the
timeframe for its emplacement and subsequent exposure. The overburden
and surrounding rocks, which at one time covered the pluton, are gone
(Figure 2). Today, when looking at Stone Mountain, two obvious questions
come to mind: Where did all the overlying and surrounding sediments
go and when did it happen?
Once again, from the creationist
perspective, the Flood event was a time of intensive tectonic (orogenic)
activity. Magma, created as a result of plate tectonic collisions and
associated heat and pressure, would have been squeezed into the overlying
rocks, causing them to be uplifted. The author believes that Flood waters
eroded away both the overlying and surrounding sediments and rock from
the quickly cooling granitic pluton. Eventually, due to the rapid erosion
which was occurring, the cooled mountain surface would be exposed to
the Flood waters which would further erode the granitic mass. With the
release of the overburden weight (which served to compress the cooling
magma mass) the mountain would expand, resulting in exfoliation. The
Flood waters might even have eroded away the outer exfoliated layers
of the exposed granitic surface.
The end of the Flood event
and subsequent draining of the waters to the ocean basins would place
the mountain and surrounding land surface at close to present conditions.
The ensuing ice age would contribute increased precipitation to the
mountain and surrounding metamorphic rock surface, resulting in the
formation of saprolite (i.e., soils) on which plant life would reestablish
itself. A oak-hickory forest climax could have developed around the
base of the mountain in as little as 150 years following the Flood,
provided that sufficient soil developed rapidly enough to support such
a forest [Figure 25] (Odum, 1971, p. 261). The reader must realize that
this is a "catastrophic" interpretation as to events which
happen during the Flood event. Many questions and issues remain to be
resolved, however, this model is a starting point.
Stone Mountain provides
witness to orogenic events of monumental proportion which have occurred
in earth's past. I believe that Stone Mountain formed and was exposed
as a result of the events associated with the Flood event described
in Genesis. The mountain we see today has not been exposed due to peneplaination,
but rather has been exposed due to erosion during and following the
Flood event. The forest which grows on and around the mountain has adapted
to the shallow nature of the saprolite or soils which have formed above
the underlying rocks from the Ice Age to present timeframe.
The Law of Cross-cutting
Relationships forms the basis for the chronological reconstruction of
an intrusive event into the surrounding country rock. However, this
law does not give an absolute age date for the event, it only gives
a "what came first" chronology, or relative date. Age dating
by radioactive techniques serves to further "refine" the age
of the rock. Age dating of Stone Mountain Granite has been done by Pinson,
Fairburn, Hurley, Herzog and Cormier (1958, pp. 58-60) and Long, Kulp
and Eckelmann (1959, pp. 585-603), using biotite and muscovite, respectively.
The biotite was analyzed using the Rubidium-Strontium method and was
found to be approximately 280 +/- 14 Ma old. The muscovite was analyzed
using the Potassium- Argon method and was approximated as 294 +/- 10
Ma old. Standard uniformitarian radioactive dating assumptions were
used in both dating techniques and both reinforce the Pennsylvanian/Permian
date presumed to be the time of intrusion.
This information is presented
to show how the Law of Cross- cutting relationships is used, in this
case, to reinforce the preexisting uniformitarian timescale. The youngest
rock cross- cut by an intrusion is older than the intrusion and serves
as the beginning point for an age date determination of the intrusion.
The scale used in age determination is the evolutionary uniformitarian
timescale. Hence any radioactive dating method used will seek to reinforce
the already accepted Pennsylvanian/Permian date.
Adamellite - A variety of
granite containing a calcium-bearing plagioclase, usually oligoclase
and a potassium feldspar in roughly equal amounts.
Anatectic/Anatexis - A high-temperature
metamorphic process by which plutonic rock in the deeper levels of the
crust is dissolved and regenerated as a magma.
Aplite - A dike rock consisting
essentially of quartz and alkali feldspar, with a fine-grained, sugary
Autolith - An inclusion
or fragment of older igneous rock that is genetically related to the
rock and has partially melted and mixed with the rock.
Country Rock - A general
term applied to rocks invaded by and surrounding an igneous intrusion.
Diabase - A rock of basaltic
composition, consisting essentially of labradorite and pyroxene, and
characterized by ophitic texture.
Dike - A tabular body of
igneous rock that cuts across the structure of adjacent rocks or cuts
massive rocks. Although most dikes result from the intrusion of magma,
some are the result of metasomatic replacement.
Dilation - The expansion
of the rock mass following the removal of the overburden confining pressure,
usually resulting in exfoliation.
Exfoliation - (also known
as spalling or sheeting) The breaking of sheets of rock from the surface
of the same rock by the action of either physical or chemical forces.
Fault - A fracture or fracture
zone along which there has been displacement of the sides relative to
one another parallel to the fracture.
Felsic - applied to light-colored
rocks containing quartz, feldspars, feldspathoids and muscovite.
Gneiss - A coarse-grained
rock in which bands rich in granular minerals alternate with bands in
which schistose minerals predominate.
Igneous - Formed by solidifaction
from a molten or partially molten state. Rocks formed in this manner
have also been called plutonic rocks.
Joint - Fracture in rock,
generally more or less vertical or transverse to bedding, along which
no appreciable movement has occurred.
Law of Cross-cutting Relationships
- A stratigraphic principle whereby relative ages of rocks can be established.
An igneous rock is younger than any rock across which it cuts.
Leucocratic - A term applied
to light-colored igneous rocks which contain from 0 to 30% dark minerals.
Mafic - Pertaining to or
composed dominantly of the magnesian rock forming silicates. Synonymous
with "dark minerals."
Metasomatism - The processes
by which one mineral is replaced by another of different chemical composition
due to reactions set up by the introduction of material from external
Migmatite - Rock consisting
of a composite of igneous or igneous looking and/or metamorphic materials.
Monadnock - A residual rock,
hill or mountain standing above a peneplain.
Monzonite - A granular plutonic
rock containing approximately equal amounts of orthoclase and plagioclase.
Ophitic - A term applied
to a texture characteristic of diabases or dolerite in which euhedral
or subhedral crystals of plagioclase are embedded in a mesostasis of
pyroxene crystals, usually augite.
Orogeny - The process of
Overburden - Material of
any nature, consolidated or unconsolidated, that overlies the geologic
object of interest.
Pegmatite - Igneous rocks
of coarse grain found usually as dikes associated with plutonic rock
of finer grain size.
Peneplain - A land surface
worn down by erosion to a nearly flat or broadly undulating plain.
Peraluminous - In the Shand
classification of igneous rocks, a division embracing those rocks in
which the molecular proportion of alumina exceeds that of soda, potash
and lime combined.
Pluton - A body of igneous
rock that has formed beneath the surface of the earth by consolidation
Saprolite - A soft, earthy,
clay-rich, thoroughly decomposed rock formed in place by chemical weathering
of igneous or metamorphic rocks.
Schist - A medium or coarse-grained
metamorphic rock with subparallel orientation of the micaceous minerals
which dominate its composition.
Schlieren - Tabular bodies,
generally a few inches to tens of feet long, that occur in plutonic
rocks. They have the same general mineralogy as the plutonic rocks,
but because of differences in mineral ratios they are darker or lighter;
the boundaries tend to be transitional.
Tectonic - Pertaining to
or designating the rock structure and external forms resulting from
the deformation of the earth's crust.
Xenolith - Rock fragments
of surrounding country rock which are unmelted in the original intrusive
The author thanks Dr. Emmett
L. Williams and the anonymous reviewers who reviewed and commented on
this article. Additionally, I thank my wife Susan for giving me time
to research and write this article.
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Figure 1. State of Georgia
with shaded areas of igneous outcrop and U.S. Geological Survey topographic
map showing elevation and features of the Stone Mountain pluton.
Figure 2. Stone Mountain
rises approximately 780 feet above the surrounding land surface. One
building on top of the mountain, seen in this picture, is six stories
Figure 3. Flow structures
seen on east end of the mountain. These structures suggest that the
granite might have been intruded in pulses, as opposed to one event.
However, the author suggests these structures indicate compression of
the granite in a semi-solid state.
Figure 4. Xenolith of banded
biotite gneiss, cross-cut by quartz-feldspar dikes. Scale in inches
Figure 5. Jointing and weathering
of granite has resulted in widening the joints and eroding the jointed
rock into blocks.
Figure 6. A mineralized
fracture (i.e., dike) pegmatite. This pegmatite contains crystals of
quartz, feldspar, muscovite and tourmaline. Scale in inches and centimeters.
Figure 7. Blended pegmatite
dike. This dike does not show sharp contact with the surrounding granite,
rather the contact grains blend together.
Figure 8. Biotite Schlieren.
Heat and pressure are believed to have modified the original xenolith
rock pieces into these biotite schlieren.
Figure 9. Joints, Fractures
and sheeting are all represented in this figure. Scale in center of
photo is 6.5 inches.
Figure 10. A spring flows
from a fracture in the granite. Several areas in the Park exhibit fracture
flowing springs following precipitation events.
Figure 11. A Tourmaline
Dike cuts through the granitic mass in a manner similar to a diabase
dike. Scale is in inches and centimeters.
Figure 12. An exfoliated
sheet of granite eventually breaks into blocks due to internal jointing
Figure 13. Blocks of granite
lie on the mountain surface. These blocks, each weighing several tons,
are completely detached from the mountain. At one time these blocks
formed another layer of granite over the mountain. Perhaps this outer
layer was removed by the Flood? The spall lying at the base of the mountain
does not calculate to what is necessary to cover the mountain with another
Figure 14. Drill holes mark
the joint which the quarry workers used to break the granite for use
as ornamental stone. Rock hammer rests on ledge in center of block,
for scale. Note also the flowing water issuing from lower sheet surface.
Figure 15. Exfoliation continues
on Stone Mountain. Large sheets break from the granitic rock mass due
to dilation, jointing and fracturing.
Figure 16. Large sheets
of exfoliated granite lie at base of mountain. These sheets of rock,
some weighing several tons, are post-Flood deposits.
Figure 17. Pit and dome
structure. Granite pavement weathers into pits and domes due to exfoliation
Figure 18. Vernal pools
atop Stone Mountain. These pools are home to unique forms of plant and
Figure 19. Secondary weathering
feature. Scale is in inches and centimeters.
Figure 20. Weathering not
only occurs along top and bottom of rock but also along the sides of
the granite. This same weathering feature is seen in granitic rock on
the Antarctic continent and is called case hardened or core softened
granitic weathering. It is believed to be caused by the freeze/thaw
cycle (Conca, 1993).
Figure 21. Tourmaline crystals
are harder than the surrounding granitic rock and as a result they weather
more slowly and create raised bumps on the granite pavement. Also note
secondary weathering patterns and dry pits.
Figure 22. White saprolite
which is derived from weathered Stone Mountain Granite. Scale is 3.5
feet (The rod in the photograph has been retouched for clarity). Saprolite
at this locale was approximately 6.5 feet thick. The top 2 feet of saprolite
has a light brown color due to organic activity.
Figure 23. Sand dome atop
Stone Mountain. Saprolite has accumulated in a depression on top of
Stone Mountain forming a dome approximately 12 feet in diameter by 2
Figure 24. Pit and dome
structure showing a sand filled vernal pool in the foreground and a
plant community in the adjacent vernal pool in the background.
Figure 25. Climax Hardwood
forest at the base of the mountain. This forest exists at the base of
the mountain in no more than 2.5 feet of soil. Trees are approximately
35 to 45 feet tall. Stone Mountain is immediately in background and
provides the dark backdrop.