WARREN. 



ALKALI-GRANITES AND PORPHYRIES. 



209 



II — Fine grained granite similar in mineral composition to I, but 

 predominately riebeckitic and of a little more basic composition. 



III — The Blue Hill Porphyries: riebeckite, aegrite bearing, quartz- 

 feldspar or granite porphyries. 



IV — Dark, alkali-feldspar- or rhombenporphyry. 



V — Cognate Xenolithes occurring in I and III. These are for 

 the most part fine grained varieties usually porphyritic and more 

 basic than the granite. 



VI — Aporhyolite. 



To these may be added, fine-granite and pegmatites, both of rare 

 occurrence. 



I. — The Coarse-Granite. 



Distribution. — Reference to the map (No. I) will show that the 

 granite, so far as its surface exposure is concerned, occupies somewhat 

 less than one-half of the exposed area and if we assume that the 

 extensive areas in the western section now covered with drift are 

 underlain by granite, which is probably the case, then the porphyries 



General map of the Quincy-Blue Hill Area. No. I. 





Coarse & -KA n it e 



±1±1J f^/}i c Q re ni Ct 



iJLLi Quc.rCi.'F:<tclsl3oy-<^ G -rci t-i, te -foi-J^^tj-ry , 



t^^ 



oZcci^e, (C ^ md y ia n), 



Coixc, /'omer-o.t: e C Ca-y ioix, /rro- . 



a a o 

 o a o 



This map is based on the regular Topographic map of the U. S. Geological 

 Survey, the only available map of the area as a whole. Although not as good 

 as could be desired it will serve to show the general location of the area in 

 question and the approximate distribution of the principal rock types. To 

 show their exact occurrence on a suitable scale would demand an expenditure 

 of time and money that are prohibitive and would serve no very useful purpose. 



