Correlation of the Lower Silurian — Ulrich. 43 
horizon is the " Orthis bed " which comes in at an elevation of 
430 to 435 feet above low^ w^ater mark. This bed is generally 
several feet in thickness and remarkable chiefly because it con- 
tains great numbers of a very large and gibbous form of Platy- 
stropkia lynx. Occasional examples of this species or variety 
are met with both above and below this bed, but none are 
known to have been found beyond the limits of beds XII. 
In Kentuckv the lower subdivision of the series of strata here 
designated as beds XII form, almost exclusively, the surface 
rock of Campbell, Kenton, Boone, Gallatin, Grant, Pendleton 
and Bracken counties. In the range of counties to the east and 
west of those mentioned the upper subdivision and a portion of 
beds XIII still remain, while the upper members of beds XI 
come to the surface over a good portion of those abutting on 
the south. They form also a rather narrow strip of surface be- 
yond the valleys of the Kentucky and Licking rivers, which, 
beginning on the western side of the group of counties men- 
tioned, passes in a rudely circular manner through the counties 
of Owen, Henry, Shelby, Spencer, Washington and the north- 
eastern portion of Marion ; as a very narrow strip through Boyle 
Into the extreme northern portion of Lincoln and the western 
portion of Garrard; from here into Madison, then on through 
Clark, Montgomery, Bath, Fleming and Mason into Bracken 
county. 
The Kentucky geologists include the lower fifty feet (all 
below the Styeptorhynchics playiocofivexzis horizon) in their 
middle Hudson, while the remaining 150 feet form the lower 
portion of their upper Hudson series.' 
In Washington, Boyle, Lincoln, Garrard, Madison and Clark 
counties the strata of this division are decidedly arenaceous, the 
feature being much more pronounced and of greater extent than 
in Ohio and Indiana. In fact some portions of the lower sub- 
divisions (which here, too, can not well be distinguished from 
the upper) may with truth be called sandstones. In these a 
* I cannot see any good palaeontological reason for the divisions pro- 
posed by the Kentuckv geologists, and have in consequence not accepted 
them. The lithological peculiarities of these three divisions disappear 
rapidly to the northward of the central counties of the state, so that in 
Ohio and Indiana their strict identification is no longer possible. 
