Invasion to Regional Metamorphism. 265 



the earlier showing much mashing, the later showing little 

 or no deformation. On the west side of the Connecticut, 

 the biotite granites and granodiorites occupy large areas, 

 are distinctly gneissoid, and are intruded by the white 

 Thomaston granites. These are almost free of dark 

 minerals, are fine-grained, and only slightly gneissoid. 

 They form some fairly large bodies, but most of them 

 form thick dikes or sheets rather than great batholiths. 

 On the east side of the Triassic valley, the red biotite 

 Branford or Stony Creek granite is younger than the 

 biotite granite gneisses. An excellent exposure m the 

 railroad cut east of Stony Creek shows how it^ has 

 shattered and intruded the older gneiss. In the vicinity 

 of the Stony Creek quarries, blocks of the older rock from 

 one or two feet up to many feet in diameter are suspended 

 in the younger granite. The latter shows marked 

 schlieren and pegmatitic structures, but here is almost 

 uncrushed. Toward Leete Island, how^ever, the younger 

 granite passes into a coarse banded gneiss with marked 

 pegmatitic habit. Large porphyritic crystals of feldspar 

 have developed between the biotite laminae, and the whole 

 is suggestive of strong deformation during and following 

 the period of primary crystallization. Aplite dikes cut 

 the coarse gneiss but have themselves been affected by 

 the pegmatization. Farther east in Connecticut, Dale has 

 described the dikes of commercial granite which cut the 

 older gneissoid granites and states that the latter are in 

 general younger than the gneisses intruded into the 

 sediments. It is possible that the granites in the east are 

 of different age from those in the west, but within each 

 province the evidence shows a genetic relationship 

 between the sequence of intrusives. This evidence is 

 found in the space relations and in the chemical relation- 

 ships. The older magmas were of the composition of 

 biotite granites or granodiorites, and developed basic 

 borders w^ith pneumatolitic structures. Within these 

 masses the younger granites were commonly restricted. 

 If the latter belonged to a wholly different cycle of 

 igneous activity, they would not be expected to show this 

 space relation but would be as likely to break across the 

 old margins and into the surrounding rocks. The compo- 

 sition also follows the usual law of differentiation and 

 points to the younger granites being the last phase in the 

 differentiation of the same magmas. The date of most 



