5 
E Hall on the Strata and Organic Remains - 
reefs, can be satisfactorily determined by the organic contents 
of the strata. 
I bave, in other connections,' lcd to point out the 
comparative developments of the different strata extending 
from the valley of the Hudson to the Mississippi River. Hav- 
ing travelled over this ground, I am acquainted, for the most 
part, with the variations in lithological and paleontological 
i eS i oe 
characters. I have also profited largely by the labors of the — 
western geologists ; and I may here again acknowledge my ob- 
ligations to Dr. Locke, Dr. Owen, Dr. Houghton, and other — 
ile i who have freely communicated to me information . 
ncerning the west. 
In this investigation we will first consider the changes in 
f. 
lithological character which these strata undergo in a westerly 
direction, as well as their greater or less development. 
. The lower rocks which the section on the Hudson valley ex- 1 
hibits and which are well developed in several parts of New | 
York, are only seen at: few points within the range of my - 
ations westward. - ne of these is at Frankfort, Ky., and — 
in n the neighborhood of that place; and the same strata, accord- - 
ing to the observations of Dr. Owen, appear upon the Mis- 
sissippi at Prairie du Chien and about the moni of Wis 
consin River. is 
At Frankfort, Ky., it is EROS 4 to say what is the com- 
parative development of the Potsdam sandstone and calciferous - | 
sandrock, but the succeeding limestones bear the same charac- | i 
ter as those of New York, and contain the same fossils. 
Upon the Mississippi, Dr. Owen has represented a sandet 
below the limestones which are the ëifuivalent of the birdseye 
and Trenton limestone. This ne holds the place, 
"and is probably the continuation of the two lower rocks of the 
inten, as seen in New York. — — 
_ 1 See section across the country from New York to the Mississippi River, Trans- 
actions Association of American Geologists and Naturalists, Vol. * P late | 
Iso, Report 
on the Geology of the 4th District, N. Y. Geol. 
E 
