prosser.] CONCLUSIONS. 71 
formations, for it is very often the case that the transition from one 
formation to another will not be sharply denned lithologically in some 
part of its area. 
The Hamilton stage as mapped and defined in Pennsylvania consists 
principally of rather coarse arenaceous shales and thin sandstones j 1 
but to these deposits should be added the calcareo-arenaceous zone 
above, called Tully limestone, and the still higher, black, fossiliferous 
shales, called the Genesee. It has been shown in this paper that the 
so-called Tully and Genesee stages of Pennsylvania do not agree with 
the ISew York formations either in lithologic or paleontologic character. 
After the disappearance of the Tully limestone and Genesee black shale 
in central New York, there is very little evidence of the reappearance 
of either in eastern New York and Pennsylvania. Since this opinion 
is the reverse of that held by the Pennsylvania geologists, a brief review 
of the data offered in support of their correlation is in order. 
Prof. White reports that "the top of the Hamilton is marked off 
everywhere in this district by the appearance of a dark, sandy fossil 
slate or shale, which seems to be identical with the Genesee black slate 
of the New York Reports. * * # It is also quite fossiliferous, con- 
taining Spirifer mucronatus, Athyris spiriferoides, Mierodon bellistriata, 
Tropidoleptus carinatus, and many other forms." 2 
As might be inferred by one familiar with the Genesee outcrops of 
New York, the so-called Genesee of Pennsylvania does not closely 
resemble the typical Genesee shales in lithologic character, but, on the 
other hand, it conspicuously resembles the Moscow zone at the top of 
the Hamilton stage. As far as the paleontology is concerned, it has 
already been shown (p. 41) that these species are not characteristic 
of the Genesee, and in fact as far as my observation has extended 
they have never been found in undisputed Genesee shale, but are char- 
acteristic of the argillaceous shales in the Upper Hamilton. Further- 
more, the difficulty of this correlation can not be removed by the sup- 
position that the above fossils were incorrectly identified, for the writer 
'Prof. Lesley, in his chapter on the "Hamilton sandstone and shale," proposes the following classi- 
fication fur the Hamilton of Pennsylvania: 
(l"i ^r '<, Moscow shales. 
i Encrinal limestone. 
Hamilton 
Middle Ludlow sandstone. 
\ Lower Skeneateles shale. 
Tn the explanat ion of this plan the professor says : " Why should not the original New York names, 
Moscow,, Skeneateles, be revived.' But if so, the original New York name for the middle division, 
viz. Ludlowville, would naturally accompany them or he adopted in the simpler form of Ludlow, 
especially as Prof. Hall justified its adoption by reference to its coincidence in time and fossils with 
the famous Ludlow formation of England." (Sum. Desc. Geol. Penn., Vol. II, p. 1237.) It is true that 
when Prof. Hall wrote his final report on the Fourth Geological District of New York in 1843 lie 
compared the Ludlowville shales with the Ludlow rocks of England, but thai was before the line 
separating the Devonian from the Upper Silurian had been determined with approximate precision, 
and such correlation was abandoned many years ago, for, as is well known, the Ludlow rocks of Eng- 
land form the upper group of the Upper Silurian, instead of belonging, with the Hamilton, to the Mid- 
dle Devonian. 
"G 6 , pp. 107, 108. 
