38 NEW YORK STATE MUSEUM 



dissolved blocks, or is not an injection elTect, it is induced by regional 

 deformation acting on the magma during its later stages of crystal- 

 lization. In some cases there are small crumples and wavy structure 

 throughout a mass which could not be affected in that manner when 

 solid. Again there are occurrences of pegmatitic facies of the same 

 rock which cut squarely across these complicated structures and 

 are not affected by them. Tihis indicates clearly that the crumpled 

 or wavy structure itself was developed before the rock had entirely 

 finished its crystallization. For the pegmatites, which are the final 

 products of the crystallization, would show the result of movement 

 if they had been solidified at the time the movement occurred. Cer- 

 tain portions of the Storm King granite as well as portions of other 

 granites, occur in this manner, and it is believed to be more common 

 than development of gneissic structure after complete solidification. 



However, deformation subsequent to recrystallization can not be 

 eliminated as a cause of gneissic structure. It is very clear that 

 there has been deformation, and there has been recrystallization 

 even in some of the most substantial rocks, but for the most part 

 these effects are either local or confined to the more incompetent 

 members. There are few evidences of extensive recrystallization 

 induced by regional metamorphism of the granites. 



Magmatic absorption or syntexis. It seems to us that an additional 

 process of very large influence is syntexis, or the absorbing of 

 country rock by invading magmas. Blocks of country rock have 

 been included as distinct xenolitlhs and probably no competen,t 

 observer would queslion either their abundance or their significance. 

 It is also clear that such xenoliths may be found in practically all 

 stages between that of almost complete independence and little modi- 

 fied condition to that of almost complete destruction. It is probable, 

 however, that not every one would be willing to believe as much as 

 we do in the complete absorption of large quantities of wall rock, 

 and to credit as much of the difference in quality within the igneous 

 mass itself to this cause. But it may indeed be, that more of what 

 appears to be a differentiation effect is really due to incomplete syn- 

 texis, with failure to redistribute the different matters that have been 

 incorporated, than to differentiation proper. It may thus happen 

 that much of the streaked and banded structure and of the divergent 

 compositions and qualities may be a sort of obscure preservation of 

 the original structure of the rock masses absorbed. Such an effect 

 might be called an antecedent structure in igneous rocks. It is neither 

 a product of differentiation nor of movement, but a structure that 



