J. D, Dana on the Quartzite, Limestone, etc. 47 
Art. VI.—On the Quartzite, Limestone and associated rocks of 
the vicinity of Great Barrington, Berkshire Co., Mass. ; by 
JAMES D. Dana. With a map. 
{Continued from vol. iv, p. 453.] 
2. From the Housatonic valley westward. 
We might naturally suppose that the succession of strata in 
Monument mountain—gneiss, quartzite, gneiss, quartzite, in 
ascending order, and 800 to 1,000 feet thick (vol. iv, p. 450)— 
would be found to characterize the formation above the Stock- 
small area, the lower mica schist is in one direction replaced by 
quartzite; the lower quartzite, in another direction, by mica 
slate ; and all the quartzite, mica schist and gneiss of the moun- 
tain, in another direction, by mica slate and chloritic mica slate, 
some of it dotted with magnetic iron. In the facts it is further 
shown that within a mile to the north of an east-and-west syn- 
clinal fold, there is a change from the one fold to two synclinals 
and an anticlinal; that several isolated north and south ranges 
of limestone are anticlinal emergences of a single burrowing 
wide-spread stratum or formation; and that some, if not all, of 
the high ridges of nearly vertically inclined mica slate, like that 
of Tom Ball, are synclinal folds of the slate. . 
In treating of the region “from the Housatonic valley west- 
ward,” I present the facts by reference to five east-and-west 
séctions in an interval of six miles. 
West of the valley in the vicinity of Housatonic village, there - 
are the following ridges and valleys (see map, repeated, wit! 
some emendations, in this volume): 1, the quartzite ridge W, 
and more to the west another, lettered L; 2, the Williamsville 
valley, continued south in Long Pond valley; 8, the Tom Ball 
ridge of mica slate; 4, 5, 6, the two limestone valleys of Alford 
separated by a mica slate ridge (Alford Ridge). 
1. A section across the Housatonic valley just below the old 
addition its continuation westward across the Williamsville 
valley and Tom Ball into Alford. It shows the anticlinal of 
the Housatonic valley (A*), with limestone outcropping from 
beneath the schist that a few hundred yards farther south covers 
it (as represented in section 1), and the schist overlaid by the 
quartzite on both sides of the river. In Williamsville valley, 
