408 J.D. Dana—Taconic Rocks and Stratigraphy. 
(4.) The limestone must be the underlying rock in general, 
for the lower and narrower portions of the Taconic range—the 
schists of which are the same in kind and: essentially con- 
tinuous. 
(5.) The above conclusions are, for like reasons, true for 
Tom Ball, Lenox Mountain, South Mountain and other minor 
ridges east of the main Taconic range in the western half of 
the Housatonic Valley, but not certainly of all. The hydro- 
mica schists and mica schists of these mountains are hence, for * 
the most part, younger than the limestones. 
2. The quartzyte, quartzytic mica schists and limestones of the 
eastern half of the limestone region.—In the eastern half of the 
Housatonic Valley, besides true or normal mica schist, there are, 
in alternating strata, as has been shown, arenaceous (quartzytic) 
mica schists, massive and bedded quartzytes, thinly bedded 
micaceous quartzytes, quartzytic gneiss or gneissic quartzyte. 
In the various sections that have been described, these rocks 
are shown to be conformable with one another and with the 
limestone; and this is the universal fact. Faults may occur 
besides those noted, and many of them not now exposed to 
view; but the conformability is a fact whatever their number. 
With reference to these rocks, the question as to which is 
normally the underlying formation, the limestone or the schists 
with the associated quartzyte, is a different one from that above 
answered, and one not admitting in all cases of so positive an 
answer. 
Some have an opinion ready in advance of investigation, 
knowing that typical Potsdam is sandstone or quartzyte, and 
assuming that the reverse is true,—that quartzyte is Potsdam 
positively. But such assumptions leave the question still for 
investigation since sand beds belong to all ages and times; and, 
further, with special pertinence here, they occur as an impor- 
tant part of the Hudson River formation in eastern New York 
at Chatham (Columbia County) and in other regions. The 
quartzytes graduate into mica schists; and so the sandstones 
of the Hudson River formation graduate into shales. Besides, 
the schists of the Taconic hills pass by gentle gradations east- 
ward into the arenaceous mica schist and quartzyte, as ex- 
plained for southern Berkshire and the adjoining towns of Con- 
necticut, on page 437 of vol. xxix, 1885. 
Many of the sections seem to leave little room for questioning 
the overlying position and Hudson River age of the quartzyte. 
In former papers,* I have presented, as evidence on this point, 
facts like those of sections 22 and 23, from opposite sides of the 
Konkaput Valley (see map); the rocks being there alike in 
kind, in stratigraphical relations, in small dip, but opposite in 
* This Journal, III, v, 33, 1873, and xiii, 45, 1877. 
