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Mineralogy and Geology. 351 
the opportunity to establish, by direct comparisons, the identity between 
the Black Slate of Michigan and that of Ohio and Indiana, and, by 
proving that it lies stratigraphically above the limestones of the Hamil- 
ton group, have established its distinction from the Marcellus shale, and 
to-ordinated it with the Genesee shale of New York. It is locally known 
ar g 
ons of the series consist of bluish, argillaceous shales and plastic clays, 
ranging in color from bluish to whitish. Numerous bands of sandstone, 
i of arenaceous magnesian limestone, from four to eighteen inches in 
“black slate” proper, of the series, is freely combustible ; and in some 
cases, where fire has been communicated by accident to outcropping 
Masses, the combustion has survived for months. By distillation, this 
shale affords petroleum and all the related compounds. Its appearance 
at the surface is generally regarded as an indication of coal, and many 
nous disappointments have resulted from ignoran 
‘ates. It is the opinion of Dr. T. S. Hunt, of the Geological Commis- 
“on of Canada, that the product issues from a bituminous limestone— 
jhe Corniferous limestone—next underlying these shales; but thoug : 
Mestone may unite its exhalations with those of the Huron group, it 
“ems more probable that the latter supplies the principal amount of Ge 
bittminous flow. It is also asserted that, at least ina few cases, petrole- 
um is eliminated in quantities of commercial importance from the rocks 
ae in the coal measures. : eg 
_ Wherever the oil-producing shales are exposed to the air, or covered 
