250 
GEOLOGY OF THE FOURTH DISTRICT 
110 . 
Fall creek, near Ithaca. From a sketch by Mrs. Hall. 
Ithaca Group. 
In the annual reports, this name was adopted for designating the highly fossiliferous shales 
and shaly sandstones, so well developed at the inclined plane of the railroad, and on the Cas- 
cadilla and Fall creeks, near Ithaca. Subsequently an examination of the highly fossilife¬ 
rous strata along the Chemung river, and particularly in Chemung county, resulted in the 
adoption of that name as designating this portion of the system. 
Succeeding examinations satisfied me of the identity of the formations at Ithaca with those 
of Chemung, and this opinion was advanced in the annual report of 1841. 
The reasons for merging the two in one, were stated to be the impossibility of identifying 
them as distinct by any characteristic fossils. The same opinion is still entertained, after a 
full examination of the strata, and a comparison of the fossils collected here and elsewhere in 
well authenticated localities of the Chemung. There is scarcely a fossil known at Ithaca, 
which is not found at numerous other localities ; though it is true, not only of Ithaca but of 
many other places, that some of the fossils are confined to the single locality in which they 
occur. 
By careful and extended examination, the Chemung group may be subdivided locally, where 
it is most perfectly developed; but these divisions will hold good only over small districts of 
country, position and lithological character having had much effect in producing these dis¬ 
tinctions dependant on fossils. Examples of this kind will be noticed under the description of 
fossils. 
