PORTAGE AND CHEMUNG GROUPS. 189 



Genesee slate. 



The first mass above the Moscow shales is the Genesee slate : it is usually colored black, 

 but often stained brown upon the outside by decomposing pyrites. Its laminae separate 

 easily, and fall to thin pieces of the size of a penny ; forming, by this kind of disintegra- 

 tion, a flat gravel. The whole mass is bituminous. Its fossils are peculiar, but few in 

 species ; yet it is not improbable that, if fresh deep cuts were made, it would be found 

 largely supplied with them. The exposure which results from weathering, obliterates 

 fossils especially when they are obscure or small. 



The lower part of the Genesee slate consists of strata or lamina? of thin slate, alternating 

 with thin-bedded compact black limestone. The thickness of the strata of limestone varies 

 from three to eighteen inches. These beds of limestone continue upwards at least one 

 hundred feet, when they disappear : above this, for three hundred feet more, the rock 

 continues a black slate ; and after this it becomes shaly, or changed into a mass in which 

 slate alternates with thin-bedded sandstone. The thin laminated masses continue onwards 

 to Portage ; and even at the Lower falls, the flags are thin-bedded, and alternate with a 

 black bituminous slate, indistinguishable from the Genesee slate at Mountmorris. The 

 strata undulate, or form short curves, which coalesce like those of the slates of the Hudson 

 river. 



Thickness of the Genesee slate. If, as we suppose, this slate succeeds the Moscow shales, 

 and if it forms the cliff at the fall near the village of Moscow, it is at least four hundred 

 feet thick. This we consider as an under estimate, rather than an over one ; for, at one 

 place near Mountmorris bridge, the exposed part is three hundred and forty feet above the 

 river. At the same time it is not improbable that undulations may exist, which must in 

 that case be set off against the dip, which amounts to fifty feet to the mile at a few points 

 where it is susceptible of measurement. 



Localities where the Genesee slate may be observed. The most important locality has al- 

 ready been noticed, namely, the great gorge above Mountmorris, through which the river 

 flows. We remark, however, that calcareous bands are numerous in the lower part, and 

 that the middle and upper portions are interlaminated with shale. Proceeding east, it 

 may be observed on Cayuga lake, south of Ludlowville, supported by the Tully limestone ; 

 at the falls of Lodi, and the outlet of Crooked lake. It forms the base of the hills of De- 

 ruyter in Madison county, and those of Fabius, Truxton and Preble. At all these places 

 it is succeeded in the ascending order by gray flags, as in the gorge of the Genesee. On 

 Lake Erie, it is well exposed and well characterized by its fossils at Eighteen-mile creek. 

 Between Lake Erie and the Genesee river, it is exposed in ravines which open to the north. 



As a general guide to the position of this rock, and the localities where it may be ob- 

 served, the student may take advantage of its position above the Hamilton shales, and its 

 general east and west range from its position at Moscow and Mountmorris. 



Thickness of the Portage group. The Portage group, as it exists in the cliffs and gorges 

 at and below Portage, is mainly a gray sandstone. So gradual has it changed from a thin 



