Invasion to Regional Metamorphism. 13 



by the similarity in composition. They show that, 

 extensive deformation and hydrothermal alteration was 

 going forward at the time of their formation. They have 

 the character and relations of a superficial series whose 

 basic nature marks the first intrusion of the batholithic 

 magmas. Such series, as seen more clearly in the Cordil- 

 leran field, accumulate as thick surface flows and breccias 

 as the first stage in the batholithic cycle. As they 

 thicken, injection into them takes place, as well as out- 

 pourings on the surface. If any of these are ancient 

 surface flows and breccias, the evidence is, so far as the 

 writer has observed, now destroyed, and it is only the 

 latest intrusive sheets w^hich show much of their original 

 nature. These are thin and somewhat limited, showing 

 in places chilled margins on both contacts. The altera- 

 tion has been a hydration and pyritization accompanying 

 and following mashing by which chlorite, serpentine, 

 quartz, calcite, and pyrite have been developed. The 

 pyritization proceeded along the joints of the more 

 resistant sheets, showing that jointing persisted in the 

 unmashed portions. Rare, thin seams of pegmatite with 

 tourmaline are found. The assemblage of phenomena 

 show alteration at only moderate depth. 



The changes in passing from central Massachusetts to 

 Long Island Sound along this resurrected Triassic floor 

 show a progressive rise through the crust from the broad 

 areas of Williamsburg granite, which Emerson regards 

 as of Carboniferous age, to comparatively superficial 

 rocks and possibly surface flows, presumably of the same 

 igneous cycle as the granites to the north. 



Now, the degree of deformation does not notably 

 change. Cleavage and close folding is dominant in the 

 southern as well as in the northern part, but the degree 

 of metamorphism is conspicuously different. Surround- 

 ing the granites, feldspathization and pegmatization 

 have occurred. Garnet, staurolite, and sillimanite are 

 developed. The sediments are transformed into coarse 

 and lustrous muscovite schists, the basic rocks into 

 amphibolites. In the south, removed from the batholiths 

 and presumably nearer the ancient surface, the argillites 

 are black slates, somewhat crumpled and lustrous, but 

 such as, if occurring in a more homogeneous formation, 

 might have supplied slates of commercial quality. The 

 impure limestones have apparently retained their car- 

 bonic acid in the presence of quartz and kaolin. The 



