306 



Scientific Geology. 



and much of it is merely mica slate which takes carbonate of limo 

 into its composition. When the carbonate is in small proportion, the 

 schistose structure of the mica slate remains : but when the mica 

 nearly disappears, the slaty structure also -vanishes, though still the 

 rock is stratified ; the dip and direction conforming to those of the 

 mica slate. It forms numerous beds in the extensive tract of mica 

 slate on the western slope of the valley of the Connecticut ; espe- 

 cially along the eastern border of the mica slate, from Whately north- 

 wards. Several beds are marked on the map, merely to indicate that 

 they are numerous, but without any intention of giving them their 

 true situation and extent. In some places, as in Whately, these beds 

 occupy half the surface ; but in general the mica slate greatly pre- 

 dominates, and for miles the limestone disappears. (Nos. 459 to 467.) 



The three varieties of this limestone from Conway and Whately, 

 mentioned in the first part of this report as having been analysed, 

 contain respectively 58, 67, and 78 per cent, of carbonate of lime. 

 More recently I have examined in the same manner a specimen from 

 Southampton, containing only 40 per cent. Another specimen from 

 Williamsburg, from a bowlder to which was attached a mass of mi- 

 ca slate, yielded 63 per cent, of the carbonate of lime. It also con- 

 tained magnesia, since its solution in nitric acid was milky. It is, 

 however, doubtful whether this specimen, (Nos. 468, 469,) ought to 

 be connected with the micaceous limestone under consideration. 



The carbonate of lime in this rock is very liable to be separated 

 from the mica and silex by the action of air and moisture, so as to 

 leave the surface of the rock coated over with a gray porous mass, 

 sometimes even several inches thick. (No. 467.) 



This rock is frequently traversed by veins of granite. (No. 465.) 

 The tortuosities of some of these veins is remarkable ; of which ex- 

 amples will be given when I come to describe granite. I have not 

 generally observed any very striking effects produced upon the lime- 

 stone by its proximity to granite. In one case, however, if I mistake 

 not, a large quantity of argentine has been produced by the action of 

 the granite on the limestone. In a very wild and unfrequented spot 

 in the northeast part of West Hampton, (not in the south part of 

 Williamsburg, as all the authorities state,) a huge mass of coarse 

 granite lies in a valley, apparently in situ. At its southern extrem- 

 ity, which is represented on the following sketch, and which is an 

 uneven perpendicular wall from 10 to 15 feet high, project the edges 

 of schistose rocks ; most of which is mica slate, but a part is mica- 



I 



