154 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
granitic in aspect, though the feldspathic element is generally 
kaolinized and the rock shows slaty partings (ibid., p. 479). At 
East Dedham a very close relation exists between the granite and 
the overlying arkose and conglomerate. Outerops on the east side of 
Mother Brook at Dedham IV, E 1 (Plate 7) and a quarter of a mile 
west at D 1 show rocks that appear as somewhat crushed or sheared 
granite but one part of the ledge at the latter locality appears gritty. 
At D 3, a few rods east of the railroad station, the rock is mostly arkosic 
but the matrix contains some small fragments of felsite and subangular, 
elongated, and subrectangular pebbles. In some places the rock at 
this locality is so granitic in appearance that it might easily be mis- 
taken for granite. A polished specimen shows the feldspar to be 
relatively fresh. In the region of Wellesley and South Natick the con- 
glomerate in the vicinity of the gramite and felsite is highly feldspathic 
and felsitic. 
Conglomerate: — Matrix. The matrix of the conglomerate through- 
out the Boston Basin consists largely of fragmentary quartz and felsite, 
the latter substance being present in almost every specimen examined. 
In addition there is a considerable percentage of feldspar and some 
quartzite, though these are by no means so universal constituents 
as the felsite. In some localities, especially at some of the Nantasket 
ledges, the matrix contains abundant epidote. In Brookline and New- 
ton, especially on the southwest side of Walnut Hill (Boston VI, B 12, 
C 13, Plate 7), the matrix of the conglomerate has been impregnated 
with basic igneous rock, probably melaphyr, so that the latter envelops 
both the grains of the matrix and some of the pebbles. 
The size of the grains is usually variable from very fine particles to 
fragments } or even 4 inch in diameter. The line of division between 
grains of the matrix and actual pebbles is often arbitrary and the rock 
in many cases grades from fine grains, less than 3); inch in diameter, 
to large pebbles or boulders several inches, or even more than a foot, in 
diameter. In only five out of fifty specimens representing different 
parts of the basin were the grains of the matrix noted as fairly uniform 
in size. 
The shape of the grains is almost universally subangular or angular. 
In only four of the specimens above mentioned were some of the grains 
rounded. 
No definite arrangement of the grains in the matrix was observed 
except that induced by shearing. ‘They were generally huddled 
together in greater or less confusion, except that in one case a rude 
stratification was noticed. 
