J. D. Dana—Taconic Rocks and Stratigraphy. 397 
ample of an obscuring of the north, west and south sides by 
both causes. Maple Hill, in West Stockbridge, has much of 
its west and north sides under deep drift—250 feet at an ore- 
bed on its northwest slope. These are examples. Long ex- 
perience in the region helps one to probable conclusions in 
many such cases, but in others, doubts will remain. In Adams 
the limit at the west foot of the Hoosac Range is one of the 
worst cases—a region of half a mile or more intervening with- 
out outcrops; and between the central quartzyte belt of the 
town and the range, it is still a question with me whether the 
quartzyte formation with its arenaceous mica schist may not 
extend for a considerable distance quite to the base of the 
mountain. ‘The first rock encountered on the ascent of that 
part of the mountain is a light colored very arenaceous mica 
schist, like beds in the quartzyte area, and also like much of 
Hoosac Mountain elsewhere. The Clarksburgh region is one 
of much doubt on account of the few outcrops. 
The quartzyte bowlders over a region are an assistance 
toward a knowledge of what is below, since they are often not 
drift bowlders, but, as explained above, masses left where they 
now are by decomposition. But again they are very deceptive 
evidence; for the region just mentioned, east and southeast of 
Adams, has striking examples of an abundance of quartzyte 
bowlders over the surface where the rock below is limestone. 
3. Stratigraphic relations. 
Limestone, hydromica schist, mica schist and quartzyte, and 
intermediate gradations between these, being the rocks within 
the limestone limits, the question is now as to their stratigraph- 
ical relations. 
1. No general overthrust faulting.—The facts with respect to 
the relative positions of the rocks here set forth require no 
allowance for possible overturns except such as affect single or 
a few associated folds. That there has been no great overturn 
affecting the region as a whole, or over a large part, is proved 
by the following characteristics of the region and its rocks. 
The gradual transition in kinds of rocks and in grade of 
metamorphism from east to west over the Taconic region; the 
like grade in the metamorphism of the limestone and the schist 
adjoining it, through all parts of the region; the absence of 
eastern rocks from the western part, and of western from the 
eastern; the gradual transitions in many cases from limestone 
to schist through impure micaceous and sandy limestones; 
these are all indubitable evidences on this point. 
Not only are the transitions from limestone to schists marked 
by micaceous, arenaceous, and other similar impurities, but 
also in many places by ferriferous conditions in both the schist 
Am. Jour. Sc1.—TuHirD Series, Vout. XXXIII, No. 196.—APRIL, 1887. 
25 
