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, an 
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 Suare. 
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 
it 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, &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, &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 
