WARREN. — ALKALI-GRANITES AND PORPHYRIES. Z/ / 



The xenoliths of the fine-granite type show Uttle evidence of grada- 

 tion into the other types, in this respect resembUng the fine-granite 

 masses in the immediate \'icinity from which they are thought to have 

 been derived. 



The xenohths found in the Pine Tree Brook Reservation, and in the 

 immediate vicinity, are essentially of the same character as those 

 already described. When we come to consider the xenoliths found in 

 the granite of Rattlesnake Hill just underneath the thick mass of 

 granite-porphyry which there covers it, we find much the same 

 characters but with certain differences. In the first place, the acute 

 habit of the feldspar phenocrysts is not noted to the same extent as in 

 the Pine Hill tract, and while there is a just as sharply marked cessa- 

 tion of the phenocry stall ine period of growth, the inner core of feldspar 

 is usually almost, if not quite, as distinctly microperthitic as the 

 feldspar of the groundmass and often almost as coarse as that of the 

 surrounding granite. The hornblende seems more highly poikilitic 

 resembling more nearly some of the hornblende in certain phases of 

 the overlying porphyry. Occasional grains of aenigmatite are also 

 present with the dark minerals, and this mineral is also found in the 

 porphyry above and in the granite. In the more siliceous xenoliths, 

 round quartz grains make their appearance in the groundmass rims 

 of the feldspar phenocrysts, and the quartz of the groundmass has also 

 a distinctly rounded habit or is even poikilitically enclosed in the 

 feldspar, a relation that is also observed in the granite-porphyry aboA'e. 

 The many dark greenish-l)lack or greenish-grey, fine-grained and non- 

 porphyritic xenoliths which occur here contain abundant aegirine- 

 augite and aegirite, together with hornblende, and although of much 

 finer grain, are texturally much the same as the surrounding granite. 

 Occasionally these show a feeble banding as if they had been drawn 

 out during inclusion in the granite. 



In general it may be said of the xenoliths which occur near the 

 contacts, that they partake to a striking degree of the mineralogical 

 and textural characteristics of the contact facies of the magma which 

 are developed oi masse in their immediate neighborhood. Though their 

 margins are moulded, and more or less invaded by the enclosing rock, 

 the actual contacts are sharp and there is no evidence of reaction be- 

 tween them, nor of any notalile transfer of material from the enclosing 

 magma to the xenolith. Their probable mode of origin as well as that 

 of the xenoliths of the normal granite will be considered later, when 

 the general process of crystallization, etc., of the magma is taken up. 



Microscopic characters of the Xenoliths of the Normal Granite. — The 



