68 NEW YORK STATE MUSEUM 



an excess of the solvents or mineralizers squeezed out by the con- 

 solidation of the surrounding granite. 



The larger bodies in the form of dikes or bosses represent real 

 intrusions of much later age than the country rock. They occur in 

 any kind of country rock, be it gneiss, schist or limestone. Con- 

 sequently they are sharply delimited on the borders, without any 

 gradation as is observed in the segregated bodies. They are off- 

 shoots of some granite mass which may be quite distant or not at all 

 in evidence at the surface. All through the western Adirondacks, 

 but particularly in St Lawrence county, dikes, veins and bosses of 

 pegmatite occur intersecting the older gneisses, and schists, with 

 only here and there a body of granite in evidence that may be 

 regarded as a source of the materials. It is very probable that much 

 of this region is underlain by a great granite bathylith of which the 

 exposed granites and pegmatites are offshoots into the overlying 

 rocks. The larger pegmatite bodies are often conspicuous features 

 in the topography, as they are very resistant to erosion and tend 

 to form knobs and ridges. They are consequently most frequently 

 encountered on the higher ground and when uncovered may be 

 visible for long distances, on account of their white color. 



