30 TRANSACTIONS OF THE [ocr. 1%, 
eastward. A small slip or fault (2) occurs here, as stated by 
Dana, and is the cause of the welling up of the cold spring; 
though the unconformability is quite small—only that which is 
often observed in sharp folds, at the contact of two rocks of 
different materials and pliability. 
Here, as usual in western Massachusetts, even the slightest 
differences in the inclination of the highly tilted layers possess 
peculiar significance. ‘That they are indications of the presence 
and axes of long sharp folds of the whole stratum, and not 
merely of unimportant plications, is shown by their general 
continuance along the strike over the whole outcrop of the dolo- 
myte. 
These observations, to my mind, therefore, appear to indicate 
a quite different stratigraphical relationship and folding of beds 
than those presented in Prof. Dana’s last paper and section on 
this subject. In place of the simple monoclinal dips shown on 
each side of the river, there would rather appear to be a long 
series of very sharp folds; at least five occur in the dolomyte 
outcrop on the eastern bank, which I have studied most care- 
fully, and are shown in my section. ‘These testify also to the 
comparative thinness of the gray magnesian bed thus crumpled, 
which could hardly be a continuation of the thick stratum of 
white Egremont marble on the west. 
I am, therefore, convinced that we must return to the view 
first proposed and later abandoned by my predecessor in this. 
field. ‘The stratigraphical evidence is very strong that the 
sheet of ‘Stockbridge limestone,” which outcrops in the white 
marble of Egremont on the west, dips entirely under the. 
Housatonic valley at Great Barrington, and then reappears only 
as the lowest members (No. 1, or Nos. 1 and 4) of the series of 
Beartown Mountain, four miles east of Great Barrington. 
The blue-gray dolomyte tracts in the Housatonic valley near 
that town probably correspond, in my view, to the ‘‘bluish 
granular limestone” (No. 7) in the upper part of the Beartown 
series. 
As to the further argument of Prof. Dana, founded on the 
relation of the associated quartzite at Great Barrington to that 
of the Ridge of Tom Ball, I have not yet examined the latter 
locality and must present my observations as they stand. 
IT. The Dolomyte Stratum at Great Barrington. 
Other reasons for the stratigraphical distinction which has 
just been made will be found, I think, in some of the character- 
istics of this local stratum. 
