GEOLOGY OF THE LONG LAKE QUADRANGLE 457 



they have been worn away from most of the region, the extent of 

 the various seas is highly conjectural. It is quite unlikely that 

 deposits of Potsdam age were ever laid down within the area of 

 the Long Lake quadrangle. But the Beekmantown waters may 

 have reached the district, it is quite likely that the Chazy waters 

 did, and that deposits of Trenton and Utica age were laid down 

 here is highly probable. The thickness which such deposits may 

 have attained here can only be guessed at, but may well have 

 amounted to several hundred feet. 



Subsequent history. At the close of the Lower Siluric the sea 

 disappeared from the region and there is no evidence that it has 

 since been submerged. It has instead been a land area, its sur- 

 face undergoing wear. The altitude above the sea has however 

 been changed from time to time, and whenever it has been increased,: 

 greater capacity has been given to the eroding agents. Many mil- 

 lions of years have passed since the close of Lower Siluric time, 

 no one can say jusi how many, and in that time every vestige of 

 the deposits of that age has disappeared from the surface of the 

 quadrangle, and the Precambric rocks beneath have also been 

 eroded somewhat. What thickness of these rocks has thus been 

 worn away can not be told, but many hundreds of feet seem to have 

 thus disappeared from the hilltops, and from looo to 2000 feet 

 more from the valleys. This is a considerable erosion, but 

 apparently of much less magnitude than the great Precambric 

 erosion. 



At the close of the Paleozoic occurred the greatest of the Post- 

 cambric disturbances of the region. Great lines of fracture were 

 formed, along which slipping, or faulting, of the rocks took place, 

 along with much minor cross faulting. The great faults have a 

 north to northeast course across the district, dividing it into a 

 great series of slices. The cross faults more or less break these up 

 into blocks of varying size, and at various levels. Some slight fold- 

 ing of the rocks also took place, but of very minor amount in com- 

 parison with the sharp folding in the New England area to the 

 eastward, and the main displacement of the district was by fault- 

 ing. Nearly all of the great faults downthrow to the east, produc- 

 ing a rude, steplike drop from the central area down to the Cham- 

 plain valley. To the eastward, in New England, folds, and large 

 faults which downthrow to the west, occur, resulting in the great 

 down-faulted trough of the valley. In the Long lake area and thence 



