10 ANNALS NEW YORK ACADEMY OF SCIENSES 



smaller undeterminable ones are present in countless numbers. Some of the 

 plagioclases show microperthitic structure. 



"Orthoclase is less abundant than the quartz and the plagioclase. Microcline 

 is rare. Biotite composes about one half of the rock. Hornblende is less in 

 amount than the quartz, its pleochroism is greeu to brown." 



Considering this description, we may establish the following points : 



1. The rocks have the same mineral composition. 



2. Texturally, they agree closely. Both are gneissic and show augen of 

 quartz and feldspar, crushed rims, interpenetration of quartz and feldspar, 

 undulatory extinction, etc. 



3. Micro-perthite is present in both. 



4. The hornblende shows the same pleochroism. 



These points seem to bring out a strong similarity in the two rocks. 

 We must remember, however, that this similarity may well exist in rocks 

 of the same group which may come from widely separated localities. 



These points of semblance are offset by the following contrasts : 



1. Quartz is very abundant in the Harrison granodiorite where it forms 

 as much as one half of the rock. In much of the Eavenswood rock, it is 

 present in small amounts and in some cases is absent entirely. 



2. The gneissic structure is present throughout the Harrison diorite, 

 but it is lacking in much of the Eavenswood rock. 



3. ISTo muscovite was found in the latter. 



4. Biotite is far more abundant in the former. 



5. No augite was described from the Harrison occurrence, and no 

 uralite was noticed. 



Considering both of the above groups of points, it seems to the writer 

 that the Eavenswood is not a continuation of the Harrison granodiorite. 

 He believes that there are two distinct igneous bodies, of which one, the 

 Harrison, has been the more thoroughly metamorphosed. 



Petrographic Laboratory, Columbia University. 



