82 CORRELATION OF GEOLOGICAL FAUNAS. [bull. 210. 
fauna dominates in the rocks above the Oneonta sandstone and on 
upward until it is finally extinguished by the deposit of red Catskill 
sediments. 
(8) Nevertheless, on tracing the strata westward, the ProducteUa 
speciosa fauna is still dominant as the Cayuga Lake meridian is 
reached, with very little trace, in the higher zones, of the Tropidoleptus 
fauna; but that the latter fauna is still living late in the sequence is 
shown by a recurrent faunule in the midst of the disjunctus fauna of 
Owego, with its Phacops rana, Tropidoleptus carina/ us, and Cypricar- 
dell a bell istr lata. 
(!>) Following the strata Avestward to the Genesee River sect ion, it 
is found that the Card tola fauna of the Portage formation has entirely 
replaced the ProducteUa speciosa fauna of Ithaca and its eastern 
equivalents. 
If now we were to interpret this into the dual nomenclature, we 
would say that the Portage formation of the Genesee Valley, with its 
Cardiola fauna, is equivalent, in the Ithaca region, to the Portage 
formation with its Spirifer Icevis fauna together with the Ithaca for- 
mation with its ProducteUa speciosa fauna, and that these latter two 
are equivalent , st rat igraphieally, to the so-called Ithaca and Oneonta 
formations of Chenango and Otsego counties, and to the upper part 
of what has been called the "Hamilton formation" in the extreme 
eastern counties of New York, holding the Spirifer mesistrialis fauna 
of that region which there extends upward to the base of the Catskill 
formation. 
CHEMUNG FORMATION AND ITS FAUNA. 
The case of the Tthaca formation and its fauna, composed of a 
majority of species of the Tropidoleptus carinatus fauna and but a 
few relatively characteristic species, leads to the inquiry: What is the 
Chemung fauna, and is it to be recognized in the eastern half of New 
York State prior to the sedimentation of the Catskill formation? These 
questions are not to be answered by examination only of those species 
of the fauna which are exhibited in the sections within the eastern 
region. We must first ascertain the content of the fauna where it is 
typically and fully represented in the western part of the State. 
In the western half of New York and across the State line in Penn- 
sylvania the Chemung formation is sharply differentiated, strati- 
graphieally, from the Hamilton formation. Between the two are 
found several hundred feet of sediments containing no trace of 
either the preceding or the following faunas. These sediments are 
divisible into two easily distinguished parts — the black Genesee shale 
and the Portage group. The lower part of the latter is typically a 
greenish argillaceous shale; its upper part is a flaggy sandstone with 
some massive sandstone beds at the top. 
The beds following the Portage sandstone contain a characteristic 
set of marine fossils which may be taken as the type of the Spirifer 
