78 NEW YORK STATE MUSEUM 



than a thousand feet, it appears that a movement of at least 2000 

 feet is determinable at this point. The displacement on the average, 

 doubtless amounts to more than this. 



The fault zone for the most part is not healed except in the lime- 

 stone. There is no very satisfactory way of determining the age of 

 this fault because nothing later than Cambro-Ordovician is involved. 

 A considerable development of formations as high as Devonian, 

 however, lies just a little farther to the west, and their position is 

 such as to prove that this faulting was subsequent to their deposition. 

 It therefore can not be earlier than the Appalachian deformation and 

 may be later than that. Considering, however, that the Triassic and 

 later types of faulting are more prominently simple block faulting, 

 this fault, which is a strikingly strong thrust type, must belong to the 

 Appalachian deformation epoch. 



No doubt there are many other similar lines in the Highlands that 

 date to the same period. It is possible indeed that some of those 

 on the south side of the Highlands are of this age and may have, 

 suffered additional movement in later time. On account of the con- 

 fusion of the geological formations within the Highlands the amount 

 of displacement is seldom determinable. There is no object in 

 undertaking a detailed description of each fault. They are numer- 

 ous and of various degrees of prominence. 



The Tompkins Covc-Pcckskill Valley fault line. The fault which 

 enters the quadrangle from the southeast at Tompkins cove forms, 

 farther south, the division line between the sandstones of the Triassic 

 lowland and the gneisses of the Highlands. It disappears, however, 

 as the principal line a few miles to the south and its place is taken by 

 a parallel fault of like habit lying to the northwest of it. This forms 

 the boundary between the gneisses and the Triassic sediments for 

 many miles in the Ramapo quadrangle of northern New Jersey. 



This fault displacement brings phyllites of essentially similar qual- 

 ity to those of Peekskill valley in contact with the granitic gneisses 

 of the Highlands. The same thing is true along the west side of 

 Peekskill valley where phyllites of Hudson River age are brought in 

 direct contact with the granite of Cat Hill and adjacent territory. It 

 appears in this case, again, that 600 feet of quartzite and 1000 feet of 

 limestone are cut out, together with a considerable amount of phyl- 

 lite, so that doubtless again 2000 feet displacement is not too much to 

 reckon. But in this case the depressed member is on the southeast 

 side and the raised member is on the northwest, just the reverse of 

 that at Storm King-Breakneck, and this result could not be obtained 

 by a thrust movement. 



