CORNIFEROUS LIMESTONE. 
175 
The following woodcut is from the Report of Mr. Vanuxem, and exhibits the prevailing 
forms in this rock in the Third District : 
3. Odontocephalus selenurus. 3. Strophomena undulata. 6 & 7. Ichthyodorulite. 
2. Cyrtoceras undulatura. 
4. Orthis lenticularis. 8. Strophomena lineata. 
5. Atrypa prisca. 
1. Odontocephalus selenurus. — The post abdomen and caudal extremity are of frequent 
occurrence in the Fourth District. 
2. Cyrtoceras undulatum. — Specimens of this genus have been seen at Waterloo, Cale¬ 
donia and Le Roy. 
3. Strophomena undulata. — This is a common fossil in many places, usually tinged of a 
reddish or bronze hue. 
3. Orthis lentiformis, has not been seen in the district. 
5. Atrypa prisca , is one of the most common and abundant fossils. 
6 & 7 . Ichthyodorulite, and section of the same. This has not been seen in the district. 
8. Strophomena lineata. — This is an abundant fossil in Seneca county, but is very rare 
farther west. 
Nos. 1, 3 and 8, may be considered as characteristic fossils in the Fourth District. 
With the termination of the Corniferous limestone end all the important limestones of the 
New-York System. The calcareous deposits which occur in a higher position are, for the most 
part, thin and rarely persistent over a great extent. The constancy and wide extent of the 
beds just described renders them one of the best horizons of reference in the whole system. 
The subsequent deposits are of a nature quite different, and the organic contents are, for the 
