1/ crick on Correlation of the Lower Silurian. 179 
A CORRELATION OF THE LOWER SILURIAN HORIZONS 
OF TENNESEE AND OF THE OHIO AND MISSISSIPPI 
VALLEYS WITH THOSE OF NEW YORK AND CANADA. 
i;V E. (). UI.KICH. 
{Ci>ii/i II 111(1 from the Ftbruary niiiiibcr.) 
Beds VIII. These beds, thoujjh \\\ both features somewhat 
variable, are easily distinouished from the precedin^^ In- their 
composition and color. Their maximum thickness in central 
Kentucky where they have been studied in iVIercer, Henry, 
and Fayette counties, is apparently not over twenty feet, and 
seems sometimes to be considerably less. The upper half, con- 
sisting^ of heavy bedded, gray, granular limestone, is the variable 
member. Its fossils also are few and liadlv preserved. The 
lower half seems more constant in its thickness, and consists of 
less coarsely granular, thin antl evenly bedded lavers. 
Some of the lavers of this division are readih decomposed 
by carl)onated waters, causing sul>terranean cavities to be formed, 
which in turn give rise to large springs. The latter sometimes 
open at the bottom of deep holes; at other times they pour in 
greater or less volume from the sides of sniall cliffs. 
The fossils, as already stated, are few and usually unfit for 
fine discrimination, being in most casc^ either roughlv silicified 
or largely destroyed by granulation. Still, in the lower portion, 
the surfaces of some of the thinnest layers are nearly filled with 
the shells of a thin and nearly flat form of .Strop/ioiiiciia, and 
other fossils. Of those that coidd be determined the following 
are of interest in this connection: 
Buthotrvpliis': siicciiU'iis Hall. (tlypioirtiiiis raiiiin'os/is r' IJill. 
GirrHm/Ihi .</. n. .xJ^'^ospiru nnn-.-iiosh-is Hall. 
Hiudia ,v/. n. Ort/iisiim .</>. a 
Beds 1 .\ . This division in its lithological characters some- 
what resembles the upper half of bed I\% and like it seems to 
be rather local in its distribution. Its thickness in Mercer and 
Boyle comities where it is more tlistinct than else^A here, is pro- 
bably not greater than fifteen feet. The layers are massive, sub- 
crystalline or granular, of a grayish color, and charged with 
cellulose chert and silicified fossils. The rock tlisintegrates ra[;- 
dly and is covered with a thick layer of light red -^oil, from wliich 
