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NEW YORK STATE MUSEUM 



which cut and are therefore younger than all the rocks of the 

 •region, up to and including the Utica formation. Their date 

 can not be fixed more definitely than this. 



On the south also there is evidence of igneous action of later 

 date than the deposition of the Utica formation. A few dikes 

 are found cutting this and the older rocks as well, which may 

 or may not be of the same age as those of the Champlain valley. 

 They are of a somewhat different sort of rock from any found 

 there, and this may possibly argue for a difference in age. None 

 of these dikes have been noted within the map limits, but three 

 outcrop along East Canada creek just east of those limits. In 

 character they show a closer relationship with some igneous rocks 



Figure 4 



of apparent post-Devonian age which occur sparsely in central 

 New York and they are probably related to them, rather than to 

 the Champlain dikes. 



Since the deposition of the Potsdam, Beekmantown, Trenton 

 and Utica formations, the region has also suffered deformation, 

 which has afi'ected them as well as the older rocks. This later 

 deformation has not been severe however. The rocks are but 

 slightly folded, but are, on the other hand, considerably faulted 

 and jointed.i This deformation period is of uncertain date except 

 that it is later than the deposition of the rocks. Quite possibly 



^A fault is produced by a sliding- movement of tlie rocks on opposite 

 sides of a fissure, with the result that the same rock stratum is higher 

 on one side than on the other, as illustrated in the accompanying diagram 

 [fig. 4]. The stratum AA has been dropped on the right side of the fault 

 relative to its position on the left side. The distance ac, measured along the 

 fault plane, is called its displacement , the vertical distance ah, that separates 

 the two ends of the stratum, is called the tliroio, and the horizontal dis- 

 tance 1)0 is the lieave of the fault. 



