90 J. D. Dana on the Quartzite, Limestone, ete. 
More to the eastward the dip increases, it being in the ledge 
called Mt. Peter (P, fig. 7), east of the principal street of the 
village, 70° to 80° to the eastward, and mostly obscure; and 
again, east of the river, toward East Mountain (a third of a 
mile east of the Berkshire House), 80° to 85° to the westward, 
with the strike nearly north, or between N. 10° E. and N. 10° 
have been unable to find evidence that this limestone 
is a continuation, in a fold, of that of Egremont. 
This Great Barrington section (fig. 7) terminates eastward in 
the slopes of East Mountain, in which the rock, a durable 
gneiss through the lower half with 120 feet of quartzite above, 
ips 60° to 50° in the outcrops nearest the limestone, diminishing 
eastward to 50° and 40°, with the strike about N. 10° E. Some 
of the outcrops of limestone and gneiss are not over ten yards 
apart. The unconformability between the gneiss and limestone 
north ; the facts need not be repeated. The stratum of mica 
schist and gneiss, s*, in Monument Mt., which becomes mica slate 
in the northwest margin of the mountain and the ridges west, 
including Tom Ball, is mica schist and gneiss again in the nage 
west of Great Barrington ; and in that east of Great Barrington 
it is a firm gneiss, breaking into huge blocks—many such cover- 
ing parts of the slopes. ese differences are due partly (a) to 
original differences in mineral composition; but partly (6), @ 
all probability, to differences in the conditions attending meta- 
morphism, such as the amount of heat, the amount of moisture 
ates the amount of pressure and of resistance to the pressure. 
one of the smooth mica slate, like that of Tom Ball and the 
Taconic Mountains, occurs in this part of Berkshire east of 
Great Barrington. 
XI. The synclinal fold in the Tom Ball ridge is at its south- 
ern end close-compres etween the limestone anticlinals, and 
dwindles out in that direction ; while, at the northern end, it 15 
broadly expanded and the limestone emerges from beneath 1t, 
the eastern and northeastern portion at a small angle. 
