48 
PALAEONTOLOGY OF NEW-YORK. 
Davenport, New-Buffalo, etc., as well as at Iowa city, Cedar rapids, 
Lime creek, Independence and elsewhere in the interior of Iowa. 
And not only do we have the same sequence from below, but in 
ascending from the Hamilton group, we find a series of green shales 
and gray and yellow sandstones, representing the Portage and Che¬ 
mung groups of New-York. 
Turning again to the eastward for comparisons, of this sequence, we 
find in the eastern part of the State of New-York, where the Hamilton 
and Chemung groups become defined, that they have an aggregate 
thickness of at least three thousand feet, and probably, in some places, 
much more. We trace the succession where the greenish olive shales 
and sandstones of the higher series are separated from the Hamilton 
group by the Genesee slate ; and following this line through Pennsyl¬ 
vania, and to the southwest from Cleveland in Ohio, we find the same 
sequence extending to the Ohio river near Portsmouth. Nor do we 
anywhere find evidences of the intercalation of another group of 
strata. 
Again, on the western side of the Cincinnati axis, we take up the 
same sequence; and from Michigan on the north we trace it to the 
Ohio river, near New-Albany. We may recognize the same sequence in 
crossing the States of Indiana and Illinois, to the Mississippi river; 
and at numerous localities in the Mississippi valley we find the same 
series of strata. 
In all the localities where I have been able to examine this series, 
the entire thickness, including some beds of Oolitic limestone at the 
summit, is less than two hundred feet. Prof. Swallow finds the same 
series in Missouri to be somewhat more*. The entire thickness, there¬ 
fore, of this group of strata on the northwestern outcrop is generally 
not more than one-fifteenth of the same in Eastern and Central New- 
York. 
* Including the fifty-five feet of lithographic limestone, which seems to me to have more intimate relations 
with the Hamilton gronp, the thickness of the Chemung group is about two hundred feet; and including 
the Hamilton group, the entire thickness is about two hundred and fifty feet. 
