ROCK FORMATION OF THE WESTERN STATES. 
513 
The great extent of almost undisturbed strata affords an opportunity for the most satisfac¬ 
tory investigations, throughout all this country. The anticlinal axis which is crossed by the 
section near Cincinnati, is an important feature. By the elevation of this axis, the higher 
rocks have been removed, and the two great coal basins of Ohio and the Wabash valley 
(formerly in all probability constituting one) are thus separated from each other. This axis 
extends in a direction northeast and southwest; and passing along the western part of Ohio, 
and crossing Lake Erie near its western extremity, it gives origin to the numerous islands of 
this part of the lake. It extends onward into Canada, and I understand from the Messrs. 
Rogers, that they have traced it far northward in that province. To the southward it passes 
through Kentucky and Tennessee, and at Frankfort, in the former State, elevates the Trenton 
and Birdseye limestones above the level of the river. 
The section crosses a synclinal axis which runs nearly parallel to the great anticlinal one, 
but its extent is unknown to me. The Wabash flows in this depression, which brings the 
coal-bearing strata below the level of the Ohio river, at its junction with the former. From 
this point the strata are seen to rise to the westward as far as the Mississippi; but beyond^ 
little is known of them. From the occurrence of extensive coal deposits in Missouri, it may 
be presumed that the strata decline to the southwest, but I have no data from actual observa¬ 
tion on which to found an opinion. 
From the necessarily hasty examinations made during this tour of exploration, which was 
extended over a large area, it was impossible to give that minuteness of detail, which is desi¬ 
rable before the subject can be considered complete. All that was attempted was to trace the 
great groups of New-York westward, and, if possible, to identify them with those known by 
different names in that part of the country. If any light has been thrown upon this question, 
or if only some few points of identity have been established, the object will have been 
accomplished. In this vast field there is room for all the laborers that can be found for half 
a century to come ; and I doubt not, from the numerous and efficient observers now at work 
in this region, upon their native or adopted soil, that all the most important details will soon 
be wrought out. 
From the want of a well defined and acknowledged basis in the West, it would always have 
been difficult, if not impossible, to establish the identity from that direction eastward; and it 
requires a knowledge of the New-York rocks, in their wide geographical range and undis¬ 
turbed position, to settle satisfactorily the place of the western rocks. 
From the facts here stated, the conclusion seems unavoidable, that the character of fossils 
is, sometimes, as variable as lithological characters ; in fact, that the species depend in some 
degree upon the nature of the material among which they lived. Fossil characters, therefore, 
become of parallel importance to the lithological; and, in order to arrive at just conclusions, 
both must be studied in connection, and localities of proximity examined. In the cases of 
the Hudson river group of shales and sandstones, in passing from New-York to Ohio, the 
lithological character is almost entirely changed ; and at the same time, also, the most promi¬ 
nent and abundant fossils are unlike those of that group in New-York. More careful exami- 
[Geol. 4th Hist.] 65 
