F.. H. Bradley—WSilurian age of the Southern Appalachians. 281 
Before giving further details of observations, it may be well 
to mention briefly the characters of the unaltered portion of at 
least the lower part of the series supposed to be represented by 
the metamorphic strata in question, beginning with the upper 
layers. 
2. Silurian of East Tennessee. 
Throughout East Tennessee the Cincinnati group is com- 
posed chiefly of shales, more or less calcareous, but includes 
generally two marked beds of limestone—the upper a red, com- 
pact, crinoidal marble; the lower, called by Safford the “ iron- 
limestone,” a strongly ferruginous rock, and so siliceous as to 
leave in many cases a tolerably solid skeleton, after its lime has 
all been removed by percolating waters, though in others, again, 
it decays entirely to a sandy clay. This lower bed is quarried, 
near Knoxville, as a flagging-stone, and proves very satisfactory, 
though its surfaces are quite irregular. Fine specimens of rip- 
ple-marks are common on these slabs; and the false-bedding of 
beach-sands is often well shown upon weathered edges of 
layers. The lowest beds of this group are generally shales. 
The total thickness has been estimated by Safford at about 
1,850 feet. 
The Trenton group is represented by heavy-bedded, red, gray 
and variegated marbles, of an estimated thickness of 380 feet, 
certain layers of which are extensively quarried and shipped for 
both building and monumental purposes. 
e Chazy—“ Maclurea beds” of Safford—consists of about 
500 feet of bluish, impure limestone, generally very shaly, 
though at some points quite solid. e usual Maclurea magna 
is quite abundant, as are also various undescribed species of 
outcrops of this series are constantly marked by vast quantities 
of cherty masses, large and small, and more or less disi - 
ted, according to the varying percentage of included dolomyte. 
This included mineral is often crystallized, and its removal 
by weathering leaves numerous rhombohedral cavities, which 
Safford has noted as peculiar to chert of this horizon. Per- 
haps, a still more constant mark is the odlitic structure, which 
