22 Geology^ ^c. of the Connecticut. 



acter of the rocks above described, as of the mica slate and 

 gneiss with which they are associated and in which they 

 sometimes form beds. 



Hornblende slate occurs on the west side of Connecticut 

 river, south of Shelburne, in Massachusetts and Connecticut, 

 also at Plainfield and Hawley. But it is not abundant or 

 well characterized generally, and is much mixed with, and 

 passes into other rocks; and therefore I have coloured it 

 only in the range from Belchertown to Guilford and from 

 Shelburne northward. Good examples of the rock contain- 

 ing quartz and some mica may be seen in the flagging stone 

 of the side walks along the eastern side of the Public Square 

 in New-Haven, and in other parts of that city. 



4. Mica Slate. 



Coloured Green. 



This is an extensive stratum in the northern part of the 

 map. On the west side of the river it forms the prevailing 

 rock; and its width continues to increase northerly, so that 

 rt occupies the principal part of Vermont. Prof. Silliman in 

 his " Tour between Hartford and Quebec," says that he 

 crossed this slate obliquely from Burlington to Hanover, a 

 distance of 84 miles, and found mica slate by far the most 

 abundant rock on the route. {Tour, &z,c. p. 386.) In Con- 

 necticut, however, along the river, this rock constitutes no ve- 

 ry broad ranges. Those which are coloured immediately in 

 contact with the secondary on both sides of the Connecticut 

 are in most places quite narrow, often not more than half a 

 mile, or even but a few rods wide, and sometimes they whol- 

 ly disappear and we pass from the sandstone immediately to 

 the hornblende slate or gneiss. 



The dip of our mica slate is variable from 20° to 90°. In 

 Vermont it is usually less than in Massachusetts; especially 

 where we first strike it in passing from the river. Farther 

 south, as in Hadley, Plainfield, Chesterfield, &i.c. it approach- 

 es 90°. East of Chesterfield the layers of this rock lean to 

 the west. Beyond Chesterfield, on the west, they lean the 

 contrary way — that is, to the east. The same is the case 

 between Chester and Westfield. This fact looks like an 

 indication of a fundamental ridge of granite, extending in 



