Notes upon the Geology of the Western States. 57 
are a few which appear to be identical with those of the carbon- 
iferous limestone of Europe, and one of these I am not able to 
distinguish from Producta hemispherica.* 
I have here already pointed out the relative position of three 
successive formations ; first, the old red sandstone group, corres- 
ponding both in its upper and lower part with the same series in 
Europe ; secondly, a limestone, which is clearly the equivalent of 
the carboniferous limestone ; and thirdly, a conglomerate which 
is the fundamental rock of the coal formation, and may therefore 
represent the millstone grit of Great Britain. It thus becomes 
quite unnecessary in this place to point out the striking similarity 
in position and other characters of the great coal formation, with 
that of Great Britain and other parts of Europe. 
Continuing the groups of New York as the standard of refer- 
ence, we next arrive, in the descending order, to the great group 
of fossiliferous shales so well developed along Cayuga and Sen- 
eca lakes, and known as Marcellus, Skaneateles, Ludlowville, 
and Moscow shales, which, for the sake of brevity, I shall speak 
of under the name of the Ludlowville group. This great group, 
Which occupies in New York a thickness not less than one thou- 
sand feet, and contains a greater number of individual fossils than 
nearly all the other groups, thins out in its western prolongation, 
losing at the same time its distinctive paleontological character, 
so that when we arrive at the falls of the Ohio, (Louisville, Ky., 
and New Albany, Ia.,) it is represented by one hundred and four 
feet of black shale,t nearly or quite destitute of fossils. Farther 
west this shale descends beneath the higher groups, and I was 
not able to discover it on the Mississippi. 
_ The “ Helderberg limestone group” follows in the order of suc- 
cession: next below is the ‘“‘ Onondaga salt group,” and below 
this, the Niagara limestone and shale group. In New York, 
these form three very distinct and important masses, extending 
Over great areas and with very considerable thickness, The first 
is in greatest force in the Helderberg mountains, in Albany 
county, and in Schoharie, where the whole thickness is four 
hundred or five hundred feet. This group gradually thins west- 
SiS ectincndcitn tee 
* I have since been able to identify eo other He sg of fossils from this rock 
with those of the carboniferous limeston Eng 
a 2 am indebted to Dr. a of New pation ri hes bored — this site 
accurate tion of its thickness. _ 
“Vol. XLIt, No. 1.—Oct. -Dee. 1841. 8 
