106 TRANSACTIONS OF THE [FeB. 23 



are not as conspicuous as would be the casein a non-crystalline 

 limestone. Still, there is a whitening of the limestone and an 

 increase in the amount of silicates, while the graj)hite scales 

 become much larger than usual. 



In the river gorge at Hailesboro the granite is very micaceous 

 and dark colored, and at the lower end of the gorge becomes 

 decidedly gneissoid. The same transitions into granulite and 

 non-micaceous varieties are also shown . 



"West of Hailesboro there is a break in the granite ridge 

 where Matoon Creek flows, and beyond this, about two miles 

 from the village, the rock shows a gradual transition into a very 

 dark variety which has the mineralogical composition of a 

 diorite though perfectly continuous with the main body of 

 granite. Several alternations between the ordinary granite and 

 the more basic phase, are seen in this vicinity. There are also 

 many dikes of jjegmatite, which ma}' be regarded as the com- 

 plement of the basic masses, the two together illustrating well 

 the tendency towards differentiation of rock magmas, which is 

 such a potent factor in the development of igneous rocks. 



The small bodies of granite which are scattered over the 

 region sometimes resemble closely the granite of the main 

 ridge, but oftener are coarse aggregates of quartz and feldspar. 

 Sometimes the grain becomes finer, and they assume the char- 

 acter of graphic granite. The ordinary granitite always occurs 

 in the form of irregular bosses, but the pegmatite, both as 

 bosses and as sharply defined dikes, cutting either gneiss, 

 limestone, or granite. The pegmatite masses are usually of 

 limited extent, but at B 4 there is an outcrop covering several 

 acres. The rock here shows, what is not uncommon elsewhere, 

 considerable tourmaline very irregularly distributed, and 

 occasionally some mica. This outcrop exhibits a perfect irrup- 

 tive contact with the limestone, like that of the main body of 

 granite described above. 



The pegmatites often show traces of metamorphism in the 

 production of incipient foliation, and the shattering of small 

 rock masses. 



Mechanical Effects of Metamorphism. — Attention has already 

 been given to certain mechanical effects of metamorphism, in 

 speaking of gneissoid structure and the brecciated sandstone. 

 But some other instances seem of sufficient interest to merit 

 description. 



At the corner of Clinton and Barney streets, in Gouverneur, 

 is an outcrop of limestone containing abundant fragments of a 

 nearly black schist. These fragments constitute, perhaps, one- 



