Williams — Gabbrqs and Diorites of the Cortlandi Series. 447 



number and relationships of these intermediate members and 

 to connect all the various types together in one geological unit 

 or " Series" the following diagram has been constructed. All 



varieties represented in the circles correspond to actual speci- 

 mens collected within the Cortlandt Area and many others 

 might have justified a still more minute differentiation. The 

 lines connecting the circles indicate the directions in which the 

 best marked transitions take place. 



These rocks present an admirable example of what are called 

 fades of a geological unit mass. In spite of their great petro- 

 graphical variety, they are everywhere connected by transi- 

 tional forms into the closest relationship. And yet we need 

 not regard all the rocks as having been formed simultane- 



