124 



GEOLOGY OF THE THIRD DISTRICT. 



the Potsdam sandstone, are the only two rocks of the district which present unahered the sand 

 of the primary region, as it appears where pure. 



The locahties of the sandstone are more numerous at the west end of the district, than at 

 the east end. 



The fossil shells in this sandstone are of an imusually large size, and in most localities 

 crowded together, and near the lower part of the rock. The most common and characteristic 

 ones in the district are Nos. 1 and 2 of the preceding wood-cut, and No. 4 of the succeeding 

 one, which represents the internal form or cavity of the Atrypa unguiformis of Mr. Conrad. 

 This truly remarkable impression in no snoall degree resembles the under part of the hoof of 

 a colt, and is often taken for such. 



This fossil cannot, consistently with what is known of the genus Atrypa, belong to it. It 

 stands alone ? but its association with two other casts in the same sandstone, and a fourth 

 in the Onondaga limestone, shows it to belong to a genus between Strophomena, Orthis and 

 Atrypa, uniting probably the three. A good name at present for the genus, will be Hippa- 

 rionix, the right meaning of which is CoWs nail, but by which we mean hoof; it being 

 a singular fact that neither the Greek or Latin language has any term for hoof, as in the 

 Saxon ; and when it shall be desirable to give precision of language to natural science, the 

 three languages must be united. 



There being but three species that we know belong to this genus, their names in the order 

 of resemblance, will be Proximate hipparionix (H. proximus), Consimilar hipparionix (H. 

 consimihs), and Similar hipparionix (H. similaris). 



29. 



1^ 



No. 4. Cut of internal part of the Proximate hipparionix. 



No. 5. Cast of the internal part of the Arenaceooa delthyria. Thia latter ca»t i> vciy abundant, and iu peculiar appearance 

 • giren riae to maojr fanciful resemblances. 



