288 NEW YORK STATE MUSEUM 



laterally between the rock layers, and bodily raising the overlying 

 rock. Here again we find two sharply contrasted sorts of lava, 

 one light colored and difficult to render thoroughly fluid, the other 

 black and fusing at a much lower temperature. Here again the 

 black rock is much the more abundant and with wider distribu- 

 tion. But here such evidence as there is shows that the black rocks 

 were the first, instead of the last to appear, as in the case of the 

 late Precambric dikes. 



In New York these rocks are confined to the near vicinity of 

 Lake Champlain, in Essex and Clinton counties. Apparently the 

 Adirondack region was on the extreme edge of the district 

 affected. 



In the Mohawk valley and westward, occasional dikes are found 

 of a very different character from those along Lake Champlain, 

 which are perhaps younger than they are and represent intrusions 

 from a different source. They are so few in number and so scat- 

 tered that they indicate only a trifling amount of igneous activity. 

 If there can be said to be any well marked center of action at all, 

 it was about Syracuse. If there were any surface volcanos, they 

 must have been few and small. 



, Paleozoic erosion 

 Throughout the latter part of the Paleozoic the Adirondack 

 region was a land area, and, if the assumption that a considerable 

 amount of the faulting of the region dates from the time of the 

 Taconic disturbance be correct, this land area had a considerable 

 elevation on the east and northeast, diminishing gradually to the 

 west and south, with the Champlain valley outlined as a result 

 of the faulting. The time involved is great, several millions of 

 years at least, and a large amount of erosion must have been 

 accomplished, specially on the more elevated areas. The cover 

 of paleozoic deposits must have been swept away over a consider- 

 able portion of the interior region, where it was thinnest, and the 

 general surface much evened by erosion. So far it has been found 

 impossible to separate this erosion interval from that which fol- 

 lowed, so far as results are concerned. All of the surface left by 



