70 COREELATION OF GEOLOGICAL FAUNAS. [bull. 210. • 
zone. a A few feet higher, in the lower part of the rocks outcropping 
in the Cascadilla Creek gorge, 6 a faunule was discovered in which 
occurred several well-known Hamilton species, among them — 
Spirifer fimbriatus. 
Pleurotomaria capillaria. 
Ambocoelia umbonata. 
Modiomorpha complanata. 
Of these only Ambocoelia belongs to the dominant Tropidoleptus 
faunal list. 
Above all these appears the typical Ithaca fauna, which now may 
be called the Productella, speciosa fauna, from the species of Produc- 
tella which is characteristic of this horizon in a number of stations 
examined and does not appear to have occurred earlier, while higher 
up it is represented by such forms as Productella lachrymosa and 
its varieties. The "Spirifer mesicostalis" associated with it in the 
fauna at Ithaca c was, at the time of writing the report, regarded as 
an early form of the species so named, then regarded as a Chemung 
species. This common Ithaca form is now called Spirifer pennatus 
var. poster us. d 
In the report'' quoted I called attention to the fact that the Ithaca 
fauna, with this Spirifer as a characteristic, occurred below the 
Chemung and was a fauna more closely related to the Hamilton than 
to the Chemung: 
This fauna is the regular successor of the Hamilton fauna, and is intermediate 
between it and that of the Chemung group. It appears to have come in from the 
east. It prevailed during the deposition of two to three hundred feet of arena- 
ceous shales; the coral sandstone fauna came in before its maximum development. 
At the close of its occupation of this area a dark, fissile shale with a Discina 
fauna came in. This I believe to be another outlier of the Genesee shale condi- 
tions, whose center at this time must have been toward the western part of the 
State. 
Since writing that report the new facts regarding the range of 
species east of the Cayuga Lake meridian have led to a recognition of 
the actual presence of a large part of the Tropidoleptus carinatus fauna 
in the sediments farther east, which are shown to be the stratigraphical 
equivalents of these beds at Ithaca. This fact establishes the varia- 
tional nature of the differences marking many of the Ithaca forms 
when compared with typical Hamilton species. Sufficient facts are 
present to show a gradation from typical Spirifer (rnucronatus) pen- 
natus of the eastern counties to Spirifer pennatus var. posterusf 
of this western extension, and many of the species going under the 
same names show some local peculiarities which are sufficient to 
« Bull. U. S. Geol. Survey No. 3, p. 14. 
Moid., p. 15. 
clbid., p. 17. 
d Palaeontology New York, Vol. VIII, Part II, p. 36, pi. 34, 189.5. 
eBull. U. S. Geol. Survey No. 3, p. 30. 
/Palaeontology New York, Vol. VIII, Part II, p. 361, figs. 27-31, PI. XXXIV. 
