FRACTURES AND DISLOCATIONS. 



137 



Another instance of a fracture, apparently more limited and local, occurs at Essex. This 

 fracture is fully illustrated and explained in my report of 1842. It is, however, so inte- 

 resting, that I subjoin a figure, with an additional explanation of its features. 



The first and most prominent character of this uplift is the upward tlirust of a thick 

 mass of the Chazy limestone through the Trenton limestone and Utica slate, the former 

 of which is adjacent and upon the south side. At the line of junction of the slate, it is 

 crushed and bent upward. The same effect has taken place upon the north side also. The 

 mass thus elevated is not less than eighty rods in width (fig. 21). 



Another change that has taken place, and which seems to stand connected with this uplift, 

 is the short fracture, first in the slate south, and next in a portion of the mass which has been 

 elevated. In the former, however, the change consists in shifts of the strata, as where 

 a particular calcareous layer is broken several times, and moved out of its original place. 

 On the other side, the thick strata of limestone are fractured, and, at each fracture, the 

 ends are bent, as at b, which may be considered either as an oscillation, or as the effect of 

 an upward moving force acting upon very limited portions of the rock, for the broken 

 masses are only about ten feet long. 



-.■■:. d e d a f, 



a. Sla'e, the layers of which have been shifted. b. Layers of limestone, wliich have been moved by oscillation. 

 d. Dyke passing through the limestone. /. Mass of limestone pushed upward. g. Crushed strata of slate. 



Phenomena of the kind just described seem to throw some light upon the mode by which 

 the slates, and many of the other rocks, have been thrown into steep dips over wide areas. 

 If, for instance, a force is applied in a very limited area, and in such a way as to break 

 and elevate the rock on one side, and at the same time leave it inclined, it would be only 

 an instance of the phenomena which have been illustrated, carried a little farther ; and in 

 order to have a wide area underlaid with steeply dipping rocks, it is only necessary that 

 the process should be repeated. We may indeed suppose that the first application of a 

 force breaks the strata as represented in the diagram ; and, afterwards, a repetition of the 

 same force, would probably result in giving an inclined position to the masses. In sup- 

 port of this view of the subject, I may refer to the changes of an analogous kind which have 

 resulted in displacing the same rocks in the valley of the Mohawk. Thus, at Tribe's hill, 

 by the side of the railroad, three uplifts occur at short intervals, as has been shown by Mr. 

 Vanuxem. His diagram is annexed,* by which it will be observed that the strata are not 



[Agricultural Report.] 



* Vanuxem's Report, p. 205. 



18 



