6 ' NEW YORK STATE MUSEUM 



the then existing surface, with manifestations of surface volcanic 

 action, we do not know, likely never can know. But not improb- 

 ably these masses may represent old reservoirs whence volcanic 

 material ascended to the surface. 



The old floor, on which the previous deposits had been laid down, 

 was largely or wholly engulfed in the molten flood, as were the old 

 deposits themselves to a large extent. These were invaded, broken 

 up, and separated into disconnected patches by the eruptive rock, 

 which then cooled and solidified far underground. There is a 

 series of these igneous intrusions with varying composition. The 

 heart of the Adirondacks felt the full force of this action. The 

 present borders were more remote from it, the igneous rocks are 

 less conspicuous there, and the old sediments occur in greater 

 mass. 



At some date after the igneous action had ceased, though proba- 

 bly commencing while it was still in progress, the rocks were sub- 

 jected to strong compression, acting mainly from one side. The 

 rocks were compressed, intricately folded, the sediments were 

 made thoroughly crystalline, all traces of their original structures 

 were obliterated, and a foliated structure was produced in them 

 and in the igneous rocks as well.^ The general process is known 

 as metamorphism. Side pressures can not produce effects such as 

 these in rocks near the surface, but only at considerable depth; 

 and, since these rocks are now at the surface, it is argued that the 

 rock covering under which they were buried at this early time 

 has been slowly and laboriously removed by erosive processes dur- 

 ing the long ages that have since elapsed. They were likely at a 

 depth of at least from 3 to 5 miles .below the surface at this time. 



The region persisted above sea level for a long time, during 

 which likely occasional movements of further uplift were in prog- 



^TJnder the temperature conditions which prevail at considerable depth 

 and specially if moisture is present, high pressure produces rearrange- 

 ment of the rock particles, mainly through recrystallization. The minerals 

 forip newly, mainly along certain dominant planes, and thus give the 

 rock a layered arrangement. In sedimentary rocks this may or may not 

 correspond with the old bedding planes. This layered arrangement of 

 the constituent minerals constitutes foliation. Often ready splitting may 

 be produced along these planes because of the concentration of a mineral 

 with good cleavage there. 



