34 NEW YORK STATE MUSEUM 



the rock which was being digested remains. Where there has been 

 failure to redistribute much of this older material, it now remains 

 as abnormal constituents of the granite and also gives structures 

 abnormal for a simple granite. These are more properly connected 

 with syntexis, a topic to be discussed later, but are mentioned here 

 as a feature particularly characterizing certain magmatic units. The 

 result of the magmatic habit emphasized in the foregoing statement 

 is to develop extensive and obscure granitic gneisses, the quality of 

 which varies with the composition of the two original rocks and 

 with the degree to which either impregnation or syntexis has devel- 

 oped. Elaborate gradation should be expected, in connection with 

 such a series, from simple dynamio-metamorphic sediments and 

 simple granites through every possible proportion of intermixed 

 gneissoid rocks. 



Other magmas appear to be somewhat less capable than the Can- 

 ada Hill of penetrating or absorbing country rock, and as a result 

 xenolithic blocks or remnants are more prominent along their 

 borders. This difference in activity of the magmas is quite inde- 

 pendent of any minor differences such as microscopic structures or 

 mineral composition, although these do aid in distinguishing the 

 individual units themselves. These small petrographic differences 

 are, as a matter of fact, the most critical of all in identifying the 

 different field units (see petrographic description), but they are not 

 the cause of the variation of the series as a whole. 



It is possible, of course, that a magma might develop great varia- 

 tion from causes such as differentiation and this is a factor to 

 be considered, but the matter belongs to another discussion. 



When magmas are less vicious or vigorous in their behavior than 

 those just discussed or when the intrusion takes place nearer the 

 surface they cut other formations more sharply. When such 

 magmas penetrate other rocks, they follow structural weaknesses 

 already established instead of soaking through the entire rock. They 

 develop complex structural features of lit-par-lit type and tongues 

 or stringers and dikes of still sharper margins, but have much less 

 capacity for impregnation or absorption of the surrounding rock 

 or of reorganizing its minerals. The Storm King granite is of this 

 type. It has marked tendency to the development of pegmatitic 

 habit within itself and may have influenced overlying formations 

 by sending emanations and similar products into them. In spite of 

 its pegmatitic tendency the formation itself lacks some of the 

 capacity of the earlier units to modify the adjacent country rock. 



