348 DIP AND STRIKE. 



It requires in many cases careful attention to discern planes of stratification in the purely granular 

 quartz of Vermont. Generally they are present, and exhibit great distinctness and regularity of stratifica- 

 tion, particularly the variety containing mica. When the mica is in small quantity, the thickness of the 

 strata is considerable ; but as the mica increases, the layers are thinner, until at length the rock becomes 

 schistose. 



In general the strike of the ledges corresponds to the strike of the formation, as well as to the adjoining 

 rocks. The question whether the quartz rock is interstratified with the Eolian limestone beneath and gneiss 



