502 H. P. CUSHING 



between the two and by the rarity of exposures showing an intru- 

 sive relation of the one with the other; (b) an intimate association 

 of syenite with Grenville in many places, as contrasted with the 

 anorthosite areas which are comparatively free from Grenville 

 inclusions ; also (c) the frequent occurrence of Grenville beds over- 

 lapping syenite in moderately undisturbed fashion, after the manner 

 of a roof. 



Because of the latter relation Bowen argues that it is difficult 

 to picture the syenite and anorthosite as conventional batholiths. 

 He says: 



It is necessary to imagine an early intrusion of a huge plug of anorthosite, 

 followed by an intrusion of syenite which took the form of a hollow cylinder, 

 circumscribing it and invading it only peripherally. All this must take place 

 without throwing the Grenville series into appressed folds, indeed without 

 significant folding of any kind. It is then necessary to imagine that erosion 

 removed every vestige of a roof from the small, interior anorthosite area, and 

 left great stretches of it throughout the broad syenite-granite belt that sur- 

 rounds it. 1 



Because such relationships seem to him improbable he suggests 

 that the Adirondack eruptive complex consists of a sheetlike mass, 

 or huge laccolith, with syenite overlying anorthosite. 



The purpose of this rejoinder is to point out that we are not 

 limited solely to the two alternatives outlined above, and that the 

 data obtained in the field seem to me definitely to contradict the 

 hypothesis that the Adirondack region is composed of a single great 

 sheetlike mass, with syenite overlying anorthosite and bearing all 

 the Grenville exposures of the region rooflike on its back. 



Distribution of anorthosite and syenite. — The Adirondack 

 anorthosite is massed in a single great body, rudely heart-shaped, 

 with the apex toward the south. There are a number of small, 

 outlying masses, some of which have some bearing on the questions 

 under discussion. But in addition the continuity of the main mass 

 is interrupted by two considerable inlying bodies of other rock, one 

 in the Lake Placid region and one near Keene. Both of these are 

 shown on the state map. At the time when Kemp prepared this 



1 Jour. Geol, XXV, No. 3, 223. 



