ONONDAGA-SALT GROUP. 



155 



Extent of the red shale in New-York. It is highly probable that it is limited to the district 

 which is indicated by the localities already cited, by which it appears to form a narrow 

 belt running parallel with, but a little south of, the Clinton group, commencing in Herki- 

 mer county, and terminating in Monroe in the vicinity of Rochester. A red shale, spotted 

 with green, rests upon the Oneida conglomerate at the High falls of the Rondout ; but this 

 seems to belong to a higher part of the group. The same red shale underlies Becraft's 

 mountain near Hudson. It only shows itself upon the east or northeast side, and then but 

 obscurely. These localities are cited, in order that observers may not be deceived by the 

 strata which so much resemble those of Onondaga county, and which form the base of 

 the plaster and salt deposits. These red beds are probably above both the plaster formation, 

 and that part of the shale which gives origin to the brine springs. 



2. Green shale, with the plaster beds. 



This portion of the group begins with red, green, drab, and yellow-colored shales alter- 

 nating several times ; the green and drab colors, however, predominate, and it is probable 

 the red may be wanting in some places. Like the lowest portion just described, it has the 

 same disposition to decompose after disintegration has taken place. In some limited places, 

 the debris of the rock is lodged upon the shelving and projecting undecomposed parts of the 

 same, like ashes, or in a light powdery condition, and having a strong bitter taste of epsom 

 or glauber salts. This portion, too, when exposed in cliffs, or when penetrated by wells, 

 shows the strata traversed by thin columnar gypsum, either white and translucent, or red- 

 dish and opake in the mass. Besides the fibrous gypsum in thin seams, selenite is not 

 uncommon, but usually in small laminated transparent masses diffused through the crum- 

 bling rock. Opake gypsum too is abundant in it, but not in beds sufficiently large for 

 quarrying ; and it may be, that in some localities, one quarter of this portion of the group 

 is a sulphate of lime. Such then are the characters of this first mass above the red shale, 

 which, however, it is proper to say, is firmer at its superior part, becoming gradually a 

 shaly limestone with thick and oval beds of plaster, and finally so sound and compact that 

 it emits a ringing sound when struck with a hard body. 



Fig. 84. 



Section of the tower green shales embracing the lower plaster beds, which appear generally as irregular seams, 



some composed of fibrous gypsum. 



a. Gypsum beds enclosed in green shales both above and below, all of which disintegrate, and then undergo a real 

 decomposition : the process may be seen in the harder shelving parts of the rock, or beneath, where the debris 

 is partially sheltered, and where there is often half a bushel of fine gray ash-like substance of a bitter taste. 



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