GEOLOGY OF THE NORTHERN ADIRONDACK REGION 289 



the former seems to have been removed later, and it can be simply 

 inferred that much wear took place. In all probability the great 

 Appalachian disturbance, near the close of the Paleozoic, must 

 have been strongly felt, causing renewed movement along the fault 

 planes provided they were in existence, and a considerable 

 increase in the altitude of the region. 



Mesozoic history 



During early Mesozoic times there were disturbances of consider- 

 able amount in the eastern part of the country, whose effects may 

 well have been felt in the Adirondack region. A subsidence of long, 

 narrow troughs, parallel to the general trend of the Appalachians, 

 took place; deposits accumulated in these troughs, often to very 

 considerable thickness ; large quantities of quite fluid igneous rock 

 ascended from below, in part reaching the surface as great flows, 

 in part thrusting a way between layers of the accumulated sedi- 

 ments as interbedded sheets; faulting on a large scale followed, 

 breaking up the surface into a great mosaic of fault blocks. It is 

 quite possible, nay probable, that further movements took jplace 

 along the Adirondack faults at this time, and additional faults 

 may have formed. It is also possible that, because of downfault- 

 ing, deposits may have accumulated in the Champlain and upper 

 Hudson valley troughs. Evidence has recently been forthcoming 

 of volcanic action, probably of this date, on the immediate south- 

 east margin of the Adirondack region, and the future may bring 

 to light similar evidence elsewhere. 



However this may be, the further faulting would have produced 

 additional elevation of the Adirondacks with increased altitude 

 above the Champlain valley, and inaugurated another period of 

 active erosion tending toward a new and lower base level. On the 

 mosaic fault blocks of the valley the amount of possible erosion 

 would largely depend on relative altitudes, and great variation in 

 the amount is to be noted on adjacent blocks, Potsdam, Beekman- 

 town, Chazy, Trenton and Utica rocks, even Precambric as well, 

 all being found as surface rocks near the lake level today, often 

 in close proximity. Where Utica rocks are at the surface, the 



