F. H.. Bradley—Silurian age of the Southern Appalachians. 288 
The maximum thicknesses are stated by Safford as: Dolomyte, 
4,000 feet; shale, 1,500 to 2,000 feet; sandstone, 1,000 
eet. At some points, the two lower members are very thin or 
even wanting. 
ext comes the Chilhowee sandstone, generally a heavy- 
bedded rock, occasionally white, generally ferruginous, often 
pyritous. This, at most of its outcrops, is metamorphosed into 
an extremely compact quartzyte, though commonly interlami- 
nated with some few thin beds of sandy shale. Scolithus bor- 
ings occur abundantly in this rock at some points; but, instead 
of this being the universal rule, as stated Safford, it is the 
exception at outcrops thus far examined by the writer. Thick- 
ness, 2,000 feet or more. As already stated, this is considered 
to be the typical Potsdam sandston 
. 
e. 
Lowest of all the recognized Silurian, we have the Ocoee 
° 
10,000 feet. 
_ While the Chilhowee and Ocoee groups, within the Tennessee 
line, may especially be considered semi-metamo hic, the sand- 
Stones of the former having been well cemented without con- 
cealing or even confusing the granular structure, the shales of 
the latter having been squeezed into smooth slates, but showing 
no crystallization, and the pebbles of its conglomerates well 
combined with the finer paste by a sort of aqueous fusion while 
yet plainly showing their pebbly character; yet lesser degrees 
of metamorphism are plainly to be traced in many of the higher 
ayers, far out into the Great Valley. Good examples of this are 
abundant in the “iron-limestone” about Knoxville, where the 
lines of original stratification are often much contorted, while 
the mass is most thoroughly compacted. 
Am, Jour. Scr.—THtRD = Vou. IX, No. 52.—Aprim, 1875. 
