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NEW YORK STATE MUSEUM 



Whether the Lorraine shales, which overlie the Utica slate in the 

 Mohawk valley, were ever deposited in the Champlain valley is 

 a question which can not at present be answered. If so, no trace 

 of them has yet been found. 



Be that as it may, the downward movement which had been 

 in progress so long, ceased after the laying down of the Utica 

 or else of the Lorraine shales, and was succeeded by a movement 

 in the contrary direction which carried the whole district above 

 sea level, where it has, for the most part, remained ever since. 



Either this upward movement was accompanied by, and likely 

 caused, by deformation; or-else deformation ensued not long after 

 the uplift. The effect was greatest in Vermont, and the result 

 there was the uplifting of the Green mountain range the rocks 

 there being considerably folded as well as faulted. In New York 

 only a slight amount of folding was produced, but extensive fault- 

 ing took place. 1 Some of these faults are easily detected and, 

 moreover, are of considerable magnitude. The Tracy brook fault, 

 for example, has a maximum throw of close to 2000 feet. It is 

 not meant to imply that there was ever that difference in level 

 at the surface on the opposite sides of the fault plane. Such 

 movements are in general so slow T that the more rapid erosion 

 on the rising side of the fault may low T er its level very materially 

 while the movement is still in progress. There is evidence also 

 of repeated movement, along some of the faults at least, down 

 to comparatively recent times, if indeed such movement is not 

 still continuing. 



l A fault is produced by a sliding movement of the 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 ac- 

 companying diagram. The 

 stratum A A 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 ab, that 

 separates the two ends of the stratum, is called the throw, and the hori- 

 zontal distance be is the heave of the fault. 



