49 Ithaca Group 49 



A comparison of the Ithaca and Portage faunas shows that 

 nearly all of the typical Portage species occur, though less abund- 

 antly, in the Ithaca fauna. Some of the most abundant species 

 of the Ithaca fauna, Cyrtina hmniltonensis and Strophodonta 

 mucronata, are present in the Portage. A few of the most dis- 

 tinctive species of the Ithaca fauna as Crypto7iella eudora and 

 Spirifer vtesacostalis, are not found in the Portage and the Ith- 

 aca shale. The prevalence of the Ithaca shale conditions and 

 the Lingula fauna probably led to the shifting of some of the 

 Portage species, since they appear to be absent from the Ithaca 

 shale; with the return of sandy sediments, the Portage species, 

 some of which were thinned almost to extin(5tion, were accom- 

 panied by Hamilton species which were probably derived from 

 the east and by others not before known from the New York 

 system, giving rise to the cosmopolitan Ithaca fauna. 



An examination of the Chemung fauna also reveals its close 

 relationship to the Ithaca fauna. Several of the species are 

 common to both. There is, however, a smaller per cent, of 

 species common to the Chemung and Ithaca, than of those com- 

 mon to the latter and the Portage fauna. This together with 

 the fadl that Portage species occur in the Ithaca group, and 

 that a typical Portage fauna occurs above the Ithaca, seem to 

 indicate that the latter has a closer relationship to the Portage 

 and shouldbe classed in the Portage epoch. 



A lylST OP THE MORE IMPORTANT PAPERS AND WORKS CON- 

 SUI.TED IN THE PREPARATION OP THIS WORK. 



1838. Hall, Jas. 2d Ann'l Rep't 4th Geol. Dist. of N. Y., 

 pp. 287-373. 



1839. Conrad, T. A. 2d Ann'l Rep't Geol. Surv. of N. Y., 

 vol. iii, pp. 57-60. 



1 841. Conrad, T. A. 5th Ann'l Rep't on the Paleont. Dep't, 

 Geol. Surv. of N. Y., vol. v, pp. 25-57. 



1842. Conrad, T. A. Obs. on Sil. & Dev. Systems of U. S., 

 with descriptions of new organic remains; Jour. Acad. Nat. 

 Sci. Phila., vol. viii, part ii, pp. 228-280. 



1842. Hall, Jas. Explanation of two sedlions at Portage; Amer. 

 Jour. Sci,, vol. xlv, pp. 329-330. 



1843. Hall, Jas. Surv. 4th Geol. Dist. of N. Y., pp. 224-227, 

 414-449. 



1846. De Verneuil, Ed. Note sur le parallelisme des roches 



