38 



There are also^ in the collection from the same forma- 

 tion several fragments too imperfect to be described of 

 Inoceramus, Bulla, Rostellaria, &c. I am inclined to think 

 this deposit holds about the same position as formation No. 

 4, of the Nebraska section,* and is probably synchronous 

 with the true chalk of the old world. 



The other rock, or at any rate the portions of it forming 

 the matrix of the fossils, has a greenish tinge, breaks with 

 a rough irregular fracture, and contains calcareous matter 

 enough to effervesce briskly in hydrochloric acid. Its struc- 

 ture is rather granilar, and some of the specimens show nu- 

 merous small rounded fragments, and an occasional larger 

 water-worn pebble, of a dark colored very compact argil- 

 laceous material, disseminated through the mass. It is 

 highly fossiliferous, though the shells are usually much dis- 

 torted by pressure,, and rarely found in a condition to give 

 a clear idea of their specific characters. The following are 

 all the species contained in the collection from this forma- 

 tion sufficiently well preserved to be characterized, viz : 

 Pholadomya (Goniomya) borealis, P. subelongata, Thracia? oc- 

 cidentalism T? subtruncata, Area {Cucullaea) equilateralis and 

 Trigonia Evansana. There are however along with these 

 other fragments, and more or less imperfect specimens of 

 bivalves, which I have not attempted to name or describe, 

 believing the practice of characterizing species from muti- 

 lated specimens retaining neither the original form nor 

 surface markings, adds nothing to science, and makes much 

 confusion. All the specimens I have seen from this rock 

 appear to belong to undescribed species. 



I regret having no information as to whether this forma- 

 tion holds a position above or below the other. The fossils 

 furnish no positive evidence that it may not be older than 



# For a section of the Nebraska rocks see a memoir by Prof. James Hall 

 and myself, in Trans. American Acad. Arts & Sci., Boston, Vol. 5, new series 

 p. 405. Also several papers by Dr. Hayden and myself, in Proceed. Acad. 

 Nat. Sci., Phila., Vol. 8. 



