img Observations on the Unification of Geological Nomenclature. 273 
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stratified with black limestones, and black shales, and gray sandstones 
having a thickness of 700 feet; succeeded by gray sandstones inter- 
stratified with black and gray argillo-arenaceous shales, and calcareo- 
arenaceous bands, and sometimes conglomerates, 700 feet; and this 
series is followed by 600 feet of conglomerate, holding limestone and 
quartz pebbles interstratified with black shale, slightly arenaceous; 
and a gray quartzose sandstone holding flakes of black and greenish 
shale, and occasional pebbles of limestone; making a total thickness 
of 2,000 feet. 
The ever-varying character of the strata may be observed in its ex- 
tension to the extreme eastern part of the continent, at Belle Isle, and 
New Foundland, and likewise westerly, by the way of Lake Huron and 
the Lake Superior region, across Wisconsin and far into Minnesota. 
In the vicinity of the trappean rocks of Lake Superior, where volcanic 
agencies are evident, it attains a thickness of 5,000 feet, and often 
consists of conglomerates composed of trappean pebbles cemented by 
a volcanic sand. In other places, it consists of white silicious sand, 
enveloping pebbles of quartz and patches of slate; and again it has 
a deep red color, and contains patches of dove-colored clay. It 
“never exhibits, in long distances, a homogeneity of structure, or uni- 
_ formity in thickness, and not unfrequently it takes into its composti- 
tion, in the upper part, particles of lime, and finally graduates into the 
overlying Calciferous. 
. It has an enormous development in the Appalachian mountains, and 
: particularly in Tennessee, where it consists, at the base, of coarse, 
eray conglomerates, talcose, chlorite and clay slates, interstratified, 
and having a semi-metamorphic aspect, and a thickness of 10,000 feet. 
In some places the conglomerate predominates over the slates, and 
has a thickness alone of 6,600 feet. This great thickness is succeeded 
by heavy-bedded sandstones, sometimes having sandy shales and thin 
flags interstratified, and containing scales of mica, and at other times 
green grains of glauconite; thickness, 2,000 feet. This is followed by 
bard, brown, greenish and gray shales, and thin sandstones, interstrati- 
fied with which are several layers of hard, dark, gray sandstone, the 
whole being 1,000 feet thick; this by soft variegated shales 2,000 feet 
_ thick; and this again by a heavy series of dolomites and limestones, 
4,000 feet in thickness; making a total thickness of 19,000 feet. Inter- 
_ stratified with the variegated shales, at intervals, are layers of blue 
limestone, which are often oolitic, and sometimes fossiliferous. 
It is well exposed in Missouri, Texas, and many places in the Rocky 
