208 J. M. Safford on the Upper Silurian Beds of Western Tenn. 
oemer. It occurs well marked at numerous points within the 
glade region and in the counties mentioned. ‘The place of this 
bed is immediately below the Devonian shales and sandstones 
cropping out, when present, from beneath those on the hill-sides. 
At many points it is the surface rock. Many of the glades, 
with naked summits, present only Niagara rocks. Some, how- 
ever, are capped by this formation. his division, as a bed, and 
looking over the whole region, is to a considerable extent cut up 
In thickness it varies much ; at some points it is entirely absent, 
No. 7 or 8 resting immediately upon the Sponge-bearing bed ; 
then again it swells out to 60 or 70 feet, and perhaps to as muc 
as 100 feet although I have not any where, as yet, measured so 
great a thickness. « Pir 
So far as it regards the particular section presented, it 1s not 
certain that No. 6is wholly, or even in part, Lower Helderberg, 
no characteristic fossils having been seen. It marks, however, 
the horizon of these rocks. Within a few miles of this point, 
the bed holding this position is well characterized in g 
sections.* 
To my mind it is evident, that this bed was subjected to very 
considerable denudation before the deposition of the Devonian 
shales and sandstone ; hence its variable thickness, or its absence 
when, in complete sections, the latter rocks are present. Going 
urther , 
furth I have reason to think that the floor of Niagara 
rocks, upon which this bed rests, was also previous] subjected, 
(but not in so great a degree,) to denudation, and h e 
* I take this opportunity of expressing thanks to friend and former 
pupil, A. B. Gant, Jr, of Cravens Mills, Wajas county, for’ valuable assistance 
investigatio and e creeks. Mr. Gant has dix 
is al and zeal promise much more with referen to the interesting 
geological features of this region. oe 
