164 Review of the New York Geological Reports. 
Art. XVIL.— Review of the New York Geological Reports. 
(Continued from p. 74, this volume.) 
Genesee Slate. (Part of F. 8 of Pennsylvania and Virginia. 
Post-medial Newer Black Slate of Rogers.) Lithologically this 
upper black slate can hardly be distinguished from the Marcellus 
shale. It isatrue “ mud” rock, composed of exceedingly fine 
argillaceous particles charged with bitumen, which imparts to it 
a deep black color, and indurated so as to possess a slaty struc- 
ture, yet not sufficiently hard to be useful as a roofing material, 
r, though when the edges above are exposed, it may resist the 
elements for a Jong time, still, when the surface is subjected to 
atmospheric vicissitudes, it soon splits, crumbles, and decays. 
The Genesee slate attains a thickness of from one hundred to 
two hundred and fifty feet, retaining a.remarkable uniformity of 
appearance and composition throughout its entire mass. 
- As usual in deposits of this nature, calcareous concretions are 
common ; they are nearly spherical and vary in diameter from a 
few inches to three feet, and lie in two ranges wide apart. Iron 
pyrites and calcareous spar are the associated minerals ; the latter 
always in the cavities of the concretions. In sheltered situations 
this formation produces saline efflorescences. Vanuxem gives 
Owing to the destructibility of this slate formation, it occupies 
a superficial area too limited to be designated on the chart by a 
particular color. Its place lies at the junction of the purple and 
brown color, and ranges nearly east and west across the state, 
from Smyrna, in Chenango county, to Lake Erie. It borders 
the margins of Cayuga and Seneca lakes, and forms high cliffs in 
the ravines above the Tully limestone. Its greatest development 
is in the gorge of the Genesee river at Mount Morris; this local- 
ity has given name to the formation. 
In the fissures of this slate, near the Tully limestone, Vanuxem 
mentions the occurrence of a sémi-crystalline rock of a blackish- 
brown color, apparently a mixture of serpentine and limestone, 
having the appearance of trap rock. | 
