MANSFIELD: ROXBURY CONGLOMERATE. 167 
Harvard Conglomerate consists of grains of quartz and small frag- 
ments of dark schist and quartzite inclosed in fine schistose material. 
The component materials vary in size from minute particles to masses 
a quarter of an inch in longest dimension. None of the grains 
appear rounded but all are either angular or subangular. The 
larger masses are scattered among the finer and all are bound in a 
silicious or micaceous cement. In thin section the matrix is highly 
schistose, consisting of quartz and mica with large crushed quartz 
grains that trail away into the finer material. 
——:— Pebbles. The pebbles consist of gray quartzite and dark 
gray schist. The dividing line between the smaller pebbles and the 
larger grains of the matrix is arbitrary, for one grades into the other. 
The pebbles ordinarily do not exceed three inches in length. ‘They 
are subangular, elongated, and irregular and some are almost round. 
No markings indicative of glacial action were observed upon them. 
Evidences of deformation are numerous. The pebbles show stretch- 
ing, with augen-structure. Some of them appear to be disconnected 
pieces of the same stratum, with rounded ends, and with augen-shaped 
pieces and fine schistose material between the separated parts. Some- 
times the pebbles look as if a sheared and stretched layer had been 
broken up into more or less rounded or oblong masses which now lie 
close together, and are more or less enveloped by finer, schistose 
fragments of the same layer. Two directions of shearing appear in 
the specimens, one parallel to the stretching and the other making an 
angle of about 45° with the first. There appears to be no well-defined 
assortment of the pebbles. In thin section a pebble of the quartzite 
is very fine and even in texture. Each grain shows some attrition 
and is subangular or even rounded. The pebble as a whole shows 
little sign of strain, though there appear to be some shear planes. 
:— Color. The main color of the Harvard Conglomerate is 
gray with greenish and whitish tints, the latter especially on weath- 
ered surfaces. In such places the matrix and the rock immediately 
below the surface are quite ferruginous. 
——:— Bedding. The features of bedding are not displayed in 
the hand specimens. 
-——:— Sandstone and Grit: A schistose greenish gray sandstone 
shading into grit accompanies the conglomerate. The sandstone is 
fine grained and the grit shades into the conglomerate. 
——:— Relations to Igneous Rocks. No igneous rocks appear in 
contact with either the conglomerate or sandstone and no rocks of such 
nature are included as pebbles in the conglomerate. 
