280 



GEOLOGY OF THE SECOND DISTRICT. 



tain, llic rock is tlie same as upon the sliore. The mountain, liowever, which is probably 

 eight hundred feet high, is composed of the members of ihc Champlain group, with tlie ex- 

 ception of the potsdam sandstone. It appears to have been raised directly up, and is verj'' 

 steep upon the west side, and upon which the following rocks are exposed, beginning with the 

 lowest, namely, Calcifcrous sandrock, Chazy and Trenton limestones, Utica slate, shales of 

 the Hudson river, thick-bedded grey and reddish sandstone, terminating in a grey limestone. 

 The last named rocks form a perpendicular mass from eighty to one hundred feet, almost in- 

 accessible on the west side. 



It- is unnecessary to describe in detail the rocks of this group again ; it will be sufficient to 

 remark that they present much the same characters as at the localities already noticed ; but 

 being compressed into a small space, we have a better chance to inspect the whole group, 

 and hence an opportunity is given for adding a few facts to those already known. 



Of the rocks which compose the great part of Snake mountain, the upper ones present some 

 characters which are unknown in Esse.x ; and, in fact, two of the members do not appear 

 upon the west side of the lake, or in this county. The middle part of this mountain is occu- 

 pied by the shales and slates of the Hudson river series, and they probably will be found four 

 hundred feet thick. The upper part, or that which is exposed under these high perpendicular 

 cliffs, is a mass of shining argillite, with some siliceous matter, traversed by irregular seams 

 of calcareous spar, the laminaj of which are quite contorted and irregularly bedded. Some of 

 the layers near the junction of the grey sandstone, or grit-rock, are composed of a soft green 

 slaty matter. The whole of the slaty mass exposed along the base of the cliff, is without 

 fossils. We find much the same appearance at the junction here, as at other places : an 

 alternation for a few feet of the two rocks, as the commencement of the one which is to suc- 

 ceed, and then the reappearance of the mass beneath ; and frequently large irregular beds, or 

 portions of strata may be observed, as in the following cut (fig. 75), where a, a, are masses 



of grit lying in the midst of the slate, insulated apparently from the mass above ; and thus 

 we find, for miles, the same general phenomena. The irregular alternations continue for ten 

 or fifteen feet, when the thick-bedded sandstone or grit appears without interruptions of this 

 kind. This mass of grit is the greywacke of authors. Some portions are brecciatcd, or 

 belong to that variety denominated rubble, by the late Prof. Eaton. The predominant color 

 of the grit is grey, but it is sometimes reddish brown. 



