J. D. Dana— Geology of Vermont and Berkshire. 39 
rock, commences on the two borders of the clay-slate area, with 
the band of the eastern border much the biases scatiaben fates 
ing in this with the general fact of a higher degree of metamor- 
phism on the east. Seventy miles farther south, in the Taconic 
Mountains, and its eastern spur, Graylock, the hydromica slate 
is in part of somewhat coarser texture and more chloritic, and 
this same rock constitutes Mount Washington in southwestern 
Massachusetts, near the southern termination of the Taconic 
range. It even becomes in part mica slate. 
The distance from the north extremity of the slate belt to 
Mount Washington, through which this small change occurs, 
is 150 miles, 
The ridges in Berkshire south of Graylock, or over the 
western third of the limestone region, including the ridges 
either side of West Stockbridge village, and the Tom Ball 
ridge farther south, west of Williamsville, consist of the same 
rocks as Graylock, with scarcely appreciable difference. Some 
of the beds are garnetiferous. 
The ridges along a line a little farther east, near the center of 
the limestone belt, that is, those next east of Tom Ball, and east 
and west of Great Barrington, have the hydromica slate replaced 
by mica schist, and then by mica schist and gneiss, part of it a 
thick-bedded granitoid gneiss. South of Great Barrington, in 
Sheffield, the schist of ridges in the midst of the limestone area 
(which has here great width) is a coarse mica schist containing 
abundantly garnets and crystals of staurolite; and the same 
staurolitic mica schist exists under similar circumstances near 
Falls Village, in Canaan, Connecticut, the next town south of 
Sheffield, and also, farther south and west, in Salisbury. Thirty 
miles south-by-west of Canaan, about Pawling, and beyond to 
the termination of the limestone belt, the associated rock is mica 
Schist or gneiss, 
mica schist, and gneiss; but only by very gradual transitions. 
It should be here kept in view that the difference in constitu- 
the presence of a few per cent (three to six) of water in the 
mica of the former, and only one or two or none in that of the 
A parallel change takes place in the associated limestone 
formation. To the north, in central Vermont, and especially 
along the western portion of the limestone region, occur the areas 
of grayish half-altered or semi-metamorphic limestone, affording 
distinguishable fossils. Further, the limestone of this northern 
