Dodge.] 
202 
[May 18, 
side of the puddingstone hills in Brighton, between Chestnut Hill 
reservoir and Washington Street, from underlying and to overly- 
ing strata, the small isolated hillocks of puddingstone at Hough’s 
Heck, with slate overlying on each side, are instances of this. 
Pebbles. Very little search among the pebbles of the pudding- 
stone, especially that of Roxbury and Horth Dorchester, has 
brought to my notice some excellent specimens in confirmation of 
the fact asserted in 1875 that our puddingstones are not the oldest 
stratified rocks of the vicinity. The best of these were from the 
following places : in Roxbury, the Tremont Street quarry ; in 
Dorchester, Percival Avenue (Meeting House Hill), the corner of 
Columbia Street and Hamilton Avenue, a new street between Law- 
rence Avenue and Quincy Street and east of Blue Hill Avenue, 
East Street, and Mt. Vernon Street. Mr. Dillerhas shown (Pro- 
ceedings, Vol. XX, pp. 366-7) that two distinct stratified groups 
occur to the north of the Boston basin, among the crystallines. 
Quartzites are very abundant among the pebbles. From what 
slight acquaintance I have with such quartzites in place, I should 
say their visible bedding is quite too massive to be often discerni- 
ble in pebbles of the size usual in our puddingstones. Microscopy 
may help here ; and its application is even more needful in the 
case of the frequent pebbles of light and dark gray which in gen- 
eral aspect resemble to the eye argillites of obscured stratification. 
There are in place among the Blue Hills large quantities of rock 
of the latter description associated with diabases (?) and, I believe 
it may be said, with stratified rocks at many points along the 
valleys and hillsides facing the valleys. 
Study of the felsites of Mattapan, massive, slaty and brec- 
ciated, leads to an active distrust of many pebbles which have a 
superficial appearance of stratification. Among the fragments 
which occur included in the mass of the last named variety of 
felsite, both the other two are represented. 
The granitic pebbles in the puddingstone are generally of a red- 
dish aspect, and if they represent familiar rocks, their original 
appearance is much modified in their present condition. 
North of the Roxbury Puddingstone. The low surface level 
and absence of outcrops over a triangular area north-east of the 
line of Tremont Street (west of the B. & P. R. R.) in Roxbury, 
