560 PROCEEDINGS OF NEW YORK MEETING. 



varies from maseive to distinctly foliated, and the contacts on adjoining rocks are 

 those of intrusive masses. 



I would call these great bodies of granite batholites, employing the word suggested 

 by Bdouard Suess, after the analogy of the word "laccolite," coined by Mr. G. K. 

 Gilbert. They have melted their way up through a great thickness of the folded strata, 

 often absorbing much of the latter into their own mass. This is well shown in the 

 central batholite in the Beries west of the Connecticut, which extends across Hatfield 

 and Williamsburg. In its eastern third it cuts through a great thickness of horn- 

 blende schists, ami i- a heavy hornblende granite. In its middle third it comes in 

 contact with less hornblende schist and with much limestone, and it is here a born- 

 blende-biotite granite. The remaining western portion is bounded and was formerly 

 covered by muscovite-biotite schists, and the granite is here white, with little biotite 

 and often much muscovite. The great mass is cut everywhere by a very great num- 

 ber of dikes of a coarse muscovite granite, which seem to represent later intrusions 

 iif the central portion of the mass into shrinkage cracks in the already cooled periph- 

 eral portions, and thus to represent more truly its original composition. 



The batholites lie in several series of ovals parallel with the strike (or these are 

 fused into single broad bands) along the centers of great synclinals, the weakening 

 along the base of the latter having furnished a favorable outlet for the fused material. 

 The Burface of contact between the granite in these batholites and the superincumbent 

 Bchists imi-i have been very irregular, and a broad area of contact metamorphosis 

 must have extended out from this surface; and the various sections presented by dif- 

 ferent erosion surfaces enable as to reconstruct the batholite with some fullness. 



Thus, in the center of the Worcester argillite is a broad oval where the argillite is 

 changed to a pure mica schisl filled with the chiastolites found in all cabinets. There 

 is no trace of granite for miles around, but 1 have no doubt that the change in 

 the argillite is due to a buried batholite, like those a few miles Bouth in the city of 

 Worcester. 



Again, where the schists are vertical, sheets may have extended deeply into the 



plastic ma88 and have retained their dip and strike because they retained their con- 

 nection with the superjacent Bchists. Thus in the Hatfield batholite, starting from 

 the hornblende schist, one finds in the line of its strike for several miles across the 

 granite fragments of the schist with true dip and strike, and. in the line' of the lime- 

 stone and the mica schist, similar fragments of these rocks. When the rocks are 

 more nearly horizontal, great Hoes of the schists float upon the granite, as the Bbrolite 

 schists on the Belchertown granite, and the Carboniferous conglomerate upon the 

 Harvard granite. 



I i zonal character of the contact metamorphosis around these batholites is in- 

 teresting, especially in aluminous Bediments. The first wave of heat develops the easily 

 formed minerals, fibrolite and chiastolite ; stronger heat, Btaurolite and game) : then 

 the first influx of alkaline waters from the granite form- pseudomorphs of these in 

 muscovite, and with increasing heat feldspars develop. So the highly altered rocks 



iresl the intrusive mass have often passed through all the stages one passes over in 

 going from the outer /.one inward. Thus, in the Carboniferous argillite in Harvard 

 ■ me finds masses of interlaced prisms of andalusite, of the largest size and finest pink 

 color, enclosing crystals of fibrolite in abundance (the two nol orientated to each 

 other), and the whole in every stage of change i" coarse muscovite. This pres< i 

 three stages which were plainly passed over in succession, and nearer the granite 



