100 TRANSACTIONS OF THE [FeB. 23 



this is sliown at B 5, where the strongly foliated gneiss passes 

 by insensible stages into coarse red granite, showing no trace 

 of banding or foliation. It is possible that the granite is 

 younger than the gneiss, the gradual passage from one to the 

 other being due to the finer grain of the intruded rock near the 

 contact and the subsequent effects of dj-uamic metamorphism. 

 But the transition is so gradual that this explanation seen)S 

 improbable, and it is rendered more so by the perfect agreement 

 in the mineralogical composition of the two rocks when 

 examined under the microscope. It seems necessary to regard 

 the gneiss and granite as different phases of the same rock. 

 The cause of the difference may be explained in two ways : 

 either the granite is an unchanged remnant of a plutonic mass 

 from which the gneiss is derived ; or it is a result of fusion of 

 the gneiss by intense metamorphism. For a choice between 

 these two explanations little evidence is at hand. It is, however, 

 a fact that the gneiss of this locality shows unusually pronounced 

 foliation, whence it Avould seem that metamorphism was strong 

 here, and would be more likely to i^roduce fusion than to leave 

 a considerable area unaffected. 



Limestone. — As shown on the map, a large portion of the 

 region examined is underlain by limestone, which extends in an 

 irregular belt many miles east and west. In age it is evidently 

 next younger than the gneiss. This limestone is the source of 

 most of the interesting minerals of the region, of which tourma- 

 line, amphibole, pyroxene, scapolite, and serpentine are, perhaps, 

 most common. But while these are developed only in certain 

 localities, the limestone nearly everywhere has disseminated 

 through it abundant scales of graphite and light brown mica, 

 sometimes associated with grains of pyrite. 



The rock varies from dark grey to white, and is always 

 coarsely crystalline. Where large surfaces are exposed a 

 . distinct banding is often apparent, but in most outcrops this is 

 not shown, and the rock presents such a massive appearance 

 that it is impossible to make out the strike and dip. Thus, in 

 spite of numerous outcrops, it is a matter of much difficulty to 

 ascertain the thickness of the formation, and its relations to the 

 underlying and overlying rocks. 



The limestone is always greatly weathered, the most evident 

 result being a gray to black surface coloration. When pyrite is 

 present a yellow stain extends to some depth. Some curious 

 effects have been produced by solution along the abundant joint 

 planes, many outcrops being completely honeycombed in this 

 way. A rounding of all edges and corners is invariably shown, 



