willi'ams] FAUNAL DISSECTION OF THE DEVONIAN. 93 
formation as the formational plane of division between the Ithaca 
and Chemung formations. But an examination of the faunas con- 
cerned makes it clear that the classification is more strongly influ- 
enced by the lithological than the paleontological evidence. 
Regarding this point Prosser 6 says: 
After reviewing the results obtained by different investigators of this problem 
of the sexiaration of the Chemung and Portage and the Chemung and Oneonta 
formations in the central part of southern New York, the facts seem to justify 
the conclusion that the Chemung begins with the Orthis im pressa fauna overlying 
the Oneonta formation. The thickness of the formation composing the Chenango 
Valley section, ranging from the base of the Marcellus shale in Sangerfield Town- 
ship, Oneida County, up into the Chemung, on top of the hill in Fenton and Kirk- 
wood townships, Broome County, to the northeast of Binghamton. is approxi- 
mately as follows: Estimating the dip for the northern part of the Chenango 
Valley to be 60 feet to the mile, we would have a thickness of about 1,500 feet for 
the Marcellus and Hamilton formations. To the east of Smyrna there are per- 
haps 25 feet, representing the Tully limestone and Genesee slate. The Sherburne 
formation is 250 feet, the Ithaca 500 feet or more, and the Oneonta 500 feet thick, 
while for the Chemung, from Greene to the top of the hill south of Port Crane, 
calling the dip 60 feet per mile, there are 1,225 feet, which result agrees quite well 
with the record of the well drilled at Binghamton. 
Generalized section giving thickness of the Chenango Valley formations. 
Feet. Feet. 
Chemung „. . 1,225 
Oneonta 550 
Ithaca '_'_ 500 f 
Sherburne 250 
Genesee and Tully 25 
Hamilton and Marcellus 1,500 (?) 
This solution is a practical one for the particular region. For the 
purpose of mapping the middle eastern part of New York the Oneonta 
sandstones may no doubt be recognized as a formation, and they form 
a convenient separating line for formations. 
When, however, the statement is made that "in the vicinity of 
Greene * * * the Oneonta beds are overlaid by a typical and 
highly developed Chemung fauna,"'' the necessity for using some o1 her 
term for the name of a fauna than the geographical name of a forma- 
tion becomes apparent, for the fauna in Greene County referred to 
doos not represent the Spirifer disjunctus fauna, which is character- 
istic of the Chemung formation in its typical geographical area. Sta- 
tistics regarding the composition of the fauna following the Oneonta 
formation in eastern New York are given by Prosser in two papers,** 
an examination of which will illustrate this fact. 
flSee Report of field work in Chenango County, by J. M. Clarke: Thirteenth Ann. Rept. New 
York State Geologist, 1893. V r ol. I, 
''The classification and distribution of the Hamilton and Chemung series of central and east 
ern New York, Part I, by C S. Prosser: Fifteenth Ann. Rept. New York State Geologist, ]»p 
165-166. 
(•Clarke, loc. cit., p. 557. 
^Classification and distribution of the Hamilton and Chemung series "f central and eastern 
New York, Part II, by Charles S. Prosser: Fifteenth Ann. Rept. New York State Geologist, L895, 
pp. 87-222. Classification and distribution of the Hamilton and Chemung series of ceni raJ and 
eastern New York, Part II, by Charles s Prosser: Seventeenth Ann. Rept. New York State 
Geologist, 1899, pp. 67-327. 
