GEOLOGY OF THE NORTHERN ADIRONDACK REGION 287 



The main faults of the region run across it with a general 

 n.n.e.-s.s.w. course, but they curve repeatedly, and a given fault 

 seldom holds a given direction for any great distance. In nearly 

 all cases the dropped block is on the east, and the raised block 

 on the west side of the fault plane. The resulting topography 

 must have consisted of relatively narrow platforms terminated 

 westward by cliffs of varying hight, depending on the throw of 

 the fault concerned, rising to the level of the next platform 

 above, the whole with a general n.n.e.-s.s.w. trend. Thus seems 

 to have been produced for the first time the considerable and 

 rather abrupt difference in level between the Adirondack region 

 and the Champlain valley. The eastern Adirondack region 

 was thus given a considerable elevation, with a rapid, steplike 

 fall to the eastward and a gentler and steadier slope to the west. 



Some few of the faults downthrow to the west instead of the 

 east, producing between such a fault and the next easterly throw- 

 ing fault to the westward a depressed block or valley with steep 

 inclosing walls on both sides. 



In addition to the main faults are a multitude of minor ones 

 grading down to the merest slight slipping along the joint planes. 

 Many of these are cross faults of considerable magnitude, making 

 large angles with the main ones, and cutting up the main plat- 

 forms into a series of segments at various levels. 



It is likely that most of these faults date from the time of the 

 Appalachian uplift of the late Paleozoic. A beginning may have 

 been made by the Taconic disturbance. 



Paleozoic igneous activity 



Initiated possibly by the disturbances which effected the eleva- 

 tion of the Taconic mountain range, though more likely of late 

 Carboniferous date, came renewed igneous action. Here again all 

 traces of surface volcanic action, if there was such, have been 

 removed by subsequent wear, and the only signs of the activity 

 which remain are the old, lava-filled channels of ascent, the dikes, 

 together with a few larger masses, which paused before reaching 

 the surface and crowded out a place for themselves by squeezing 



