10 TWELFTH ANNUAL REPORT. 



Letter of professor H. S. Williams. 



Ithaca, N. Y. Sept. U, 1883. 

 My dear professor: 



I have examined the fossils which you sent me and enquire par- 

 ticularly about in your letter received a few days ago. The fossils 

 are in very imperfect condition; and the identification cannot be 

 regarded as anything more than strongly probable. 



I find in the lot, No. 2699, from Gregson's mill, these species. 



L Productella truncata, Hall. 



2. A minute lamellibranch, like a small Aviculopecten. 



3. A minute brachiopod; oval, the smooth surface resembling 

 a dorsal valve of Ambocselia, or (?) a Nucleospira. 



The second lot. No. 2698, Cedar valley. Mower county, resembles 

 lithologically the first, but the fossils are distinct. They are: 



1. Numerous cavities of Aulopora, or some allied form. 



2. A small shell like Atrypa reticularis. 



3. A small shell like Atrypa aspera. 



4. Cyrtina, like C. Dalmani, but may be C, Hamiltonensis. 



5. Several lenticular-shaped shells which are probably Nucleo- 

 spira. 



6. A minute terebratuloid shell of Rensselceria type. 



7. Trace of a crinoid stem. 



8. Trace of a minute Orthoceras, or (?) Coleolus. 



You ask my opinion of the horizon. The material is very unsatis- 

 factory for basing a judgment on; but if the two lots are from the 

 same horizon, it is safe to say that it is lower Devonian. 



Taking the fauna of No, 2698 alone, I see nothing to prevent its 

 being Upper Silurian. 



If the two lots are from the same rock, I should think from study 

 of the fossils that the horizon is not higher than the base of the 

 Hamilton period, nor lower than the Lower Helderberg; and my 

 opinion is that the fauna belongs to an horizon near the base of 

 the Hamilton, either below it or in an equivalent position to the 

 New York Marcellus. The only really satisfactory fossil is the 

 Productella truncata; and if the brachiopods of No. 2698 came 

 from a stratum under that containing No, 2699, the No. 2698 lot 

 might occur anywhere from the Hamilton down to the Lower Hel- 

 derberg. 



Nucleospira, Rensselaeria type of terebratuloids, Cyrtinas and 

 Atrypas are genera passing from Upper Silurian through lower 



