1881.] 
201 
[Dodge. 
tals, some so small as to be invisible without the aid of a lens. 
This well is still in progress. 1 
Southward along the Neck, rock is frequently reached at depths 
varying from 175 to 200 feet. 
Roxbury Puddingstone. It seems to be substantially certain 
that the conglomerate lying in Newton, West Roxbury, Roxbury, 
and Dorchester in a band about three miles wide in Eastern 
Newton and Brookline, one and three-quarters at the shore of the 
harbor, and about equally distributed on either side of a median 
line drawn through the Five Corners in Dorchester, and the south- 
ern border of Jamaica Pond, underlies a large series of alterna- 
ting sandstones, slates and puddingstones. New exposures every 
year are making possible more complete definition of the extent 
of all the members of the group and the relations which exist 
between them. The series is eminently one of shore and shallow 
water deposits. 
While the upper strata dip steeply away from the central con- 
glomerate, much of the latter lies in a nearly horizontal position 
with a slight easterly dip occasionally observable. The exposures 
of the puddingstone occur at heights ranging from 35 to 120 feet 
or more above the city base. Throughout the Boston basin, while 
the puddingstone usually forms high conspicuous masses wherever 
it occurs, by reason of the resistance to erosion of which the 
quartz and felsite pebbles and the scarcely less hard cementing 
material are capable, the associated slates, unless supported by 
intrusions of harder rock, invariably occupy lower ground if of 
such thickness as to extend beyond the protection of the coarser 
rock. So constant is this condition, excepting where under ex- 
posure to the direct action of the sea the order of the capabilities 
of endurance of the two kinds is reversed, that surface contours 
are a valuable indication of the probable nature of rocks which 
are concealed by drift gravel. 
The southward passage from puddingstone to slate along a line 
across Savin Hill, Dorchester and West Roxbury, the passage in 
each direction from the anticlinal of slate to puddingstone in the 
Neponset valley at Lower Mills, the northward passage on each 
1 It had reached a depth of 2240 feet in October, 1881. 
