WILLIAMS. 
SHIFTING OF FAUNAS. 99 
the east toward the west during the time of the sedimentation of 
the Portage and Ithaca formations of the Cayuga Lake meridian 
was suggested by the fact that in the neighborhood of Ithaca, on 
passing upward from the Genesee shale, there is an increase of 
species of the Tropidoleptus fauna with the withdrawal of the Portage 
species. The shifting was reversed after the center of the Ithaca 
formation was passed, as was shown by the reappearance of the 
species of the Portage formation (in reverse order) on ascending the 
strata, until above the Ithaca formation, with its dominant marine 
invertebrate fauna, came several hundred feet of sediments quite 
similar to the typical Portage of western New York and holding the 
Cardiola speciosa fauna. 
This shifting of the fauna first westward and then eastward was 
such as to make the true succession of the faunas Lake a wedge-shaped 
position in the sediments rather than make a continuous superposi- 
tion of formations in one column. The Oneonta formation pushed 
westward into the midst of the Ithaca formation of Ithaca, and as it 
ceased as a formation, by the withdrawal eastward again of the 
peculiar kind of sedimentation, the Ithaca formation also pushed 
eastward, but the fauna in the latter expressed a later stage of evolu- 
tion in Chenango County than in Tompkins County. 
Taking this view of the case the Oneonta formation is, stratigraph- 
ically, at the same horizon as the middle of the Ithaca formation of 
the Ithaca section, which is also at the same horizon as the midst of the 
Portage formation of the Genesee Valley section. The fossiliferous 
zone above the Oneonta, in Chenango and Otsego counties, is the strati- 
graphical equivalent of the barren 300 or 400 feet of the Ithaca sec- 
tion and the fossiliferous beds of Caroline, which lie between the 
fossiliferous Ithaca formation with the Produciella speciosa fauna 
and the Chemung formation with the Spirifer disjunctus fauna. 
The geographical shifting of faunas coincidently with the accumu- 
lation of sediments not only is consistent wit li all I he facts which 
have so far come to light, but there is no other theory advanced by 
which the bewildering confusion in the relations of the faunas of this 
region is satisfactorily accounted for. 
The place of the Oneonta sedimentation is recognized in ihe sand- 
stones and flags in the midst of the Ithaca format ion, and 1 he Oneonta, 
by its becoming thicker and more strongly marked on passing east- 
ward in Chenango and Otsego count ies, is seen to have its origin from 
that direction. 
The black shales of the Genesee and the following line mud shales 
of the Portage of western New York containing the Cardiola fauna 
(Glyptocardia speciosa) thin out eastward; but the proposition that 
they occupy the place of the Portage and Ithaca formations of the 
central part of the State, in which is a fauna rich in species of the 
Tropidoleptus fauna, is proved by the statistics collected by Messrs. 
Prosser and Clarke. 
