48 J. D. Dana—Geology of Vermont and Berkshire. 
fourth of a mile. But toward the west end of the series, in 
front of the conformable outcrops, that is, a little nearer the 
middle of the valley, there is a ledge with a dip of 80° to 85°, 
instead of 25° or 30°. Its little extent shows that it is one of 
the local exceptions. And this is made more manifest, and its 
existence partly explained, by the fact that in the same trans- 
verse line across the flat valley, and just beyond its middle, 
there is a hill of schist whose beds dip 50° to the westward, 
instead of the usual 25° or less. The schist in the mountains 
forming the sides of the valley has little variation in dip for 
several miles. 
The reason for these irregularities is to be found in the 
inflexibility of unerystalline limestone as compared with other 
uncrystalline rocks (shales and sandstones) and its tendency, 
therefore, to break and become irregularly shoved up under 
uplifting or flexing action. Moreover, the limestone areas 
appear generally to be regions of anticlinals, and the schist 
areas those of synclinals; and the former, whatever the rock, 
are usually the places of greatest surface fractures, and the 
latter, of least. In the synclinal, the limestone beds are kept 
in place beneath the overlying strata; and therefore, the irreg- 
ularities in the limestone should not appear close to the schist. 
In such a region of extensive upturning and mountain-mak- 
ing as that of the Green Mountains there must be many lines 
of great fractures and faults. Yet the only case of non-con- 
formity in dip adjoining a ridge of schist which I have observed 
occurs near the middle of the limestone region within half a 
mile east of Great Barrington village at the foot of the section 
represented in fig. 12. The limestone dips 80° to 85° to the . 
westward ; and the schist, at its nearest outcrop—1l0 yards— 
dips 50° to 60° to the eastward, the strike being N. 10° E. 
The schist is mostly a thick-bedded gneiss; and its antique 
look and massiveness, with its contorted texture, led me, in 
view of the non-conformity of dip, to suspect actual uncon- 
formability, and also difference in age and system of uplift. 
But this idea was soon set aside by the discovery that the top of 
the ridge was made partly of quartzyte, like that of Monument 
Mountain three miles north, and by other facts showing that — 
both the schist and quartzyte were part of the limestone series. 
The facts here brought forward fully establish the conclusion 
that the limestone, quartzyte, and schists under consideration 
have the same stratigraphical relations in Berkshire that they 
have in Vermont. They therefore sustain the view that these 
formations constitute together a conformable series; and, also, 
that the area they cover is geologically one. 
[To be continued. } 
