THE ANORTHOSITE BODY IN THE ADIRONDACKS 509 



conception of a cylinder of syenite enfolding anorthosite is therefore 

 neither a necessary nor a true one; rather, there are a number of 

 separate syenite masses. 



ADIRONDACK INTRUSIVES 



N. L. BOWEN 

 Geophysical Laboratory, Carnegie Institution of Washington 



In his paper on the "Structure of the Anorthosite Body in the 

 Adirondack^ " Professor Cushing offers some objections to the 

 interpretation of Adirondack igneous geology that was given by 

 me in the paper "The Problem of the Anorthosites," and he has 

 kindly asked me to comment upon his objections. It naturally 

 gives me considerable satisfaction that an investigator with Pro- 

 fessor Cushing's broad experience of Adirondack geology should 

 accept the more important and vital aspects of my interpretation 

 of the genesis of Adirondack igneous types. I therefore find myself 

 disinclined to object very vigorously to his remarks on features 

 of Adirondack structure concerning which he finds it necessary 

 to disagree with me. This is especially true since it would be 

 presumptuous on my part to differ from him on any point involving 

 actual knowledge of field facts. Nevertheless, there seem to be 

 certain questions of interpretation on which there is room for 

 alternative views. 



The common, basic border phase of the anorthosite Professor 

 Cushing considers fatal to the idea of the extension of that rock 

 type laterally as a sheetlike mass beyond the limits of its present 

 exposure. He accepts Daly's interpretation of this border phase 

 as a chilled portion and considers that this phase must 'be the 

 outer limit of the anorthosite. I, too, accept Daly's interpretation 

 of the basic border, but consider that it is not necessarily an outer 

 limit; it may be an upper limit, or rather a former upper limit. 

 It may therefore represent a chilled upper portion of a laccolithic 

 mass extending far beyond the limits of its present exposure. 



It is perhaps necessary to go into this matter in greater detail, 

 and, in order that this may be done, mention will first be made of 



