MANSFIELD: ROXBURY CONGLOMERATE. 152 
stratification has been observed among the pebbles and a tendency 
to an arrangement with their long axes parallel. But usually no such 
features are to be observed. In general there seems to have been but 
little sorting, materials of many sizes and shapes often occurring at 
the same locality. Two extreme cases in this respect are the localities 
at Squantum and at Huit’s Cove, already mentioned. There pebbles 
and boulders of all sizes and shapes are huddled together in great 
confusion. A field occurrence of the Squantum conglomerate is 
shown in Plate 3. 
——:—Color. The color of the conglomerate presents varying 
tints in different combinations. Out of 50 representative specimens 
the following tints were present either singly or in combination, in the 
accompanying number of specimens: gray, 26; green, 20; purple, 
19; drab, 9 ; red, 4; pink, 4; blue, 1.: If red and pink are classed 
with purple it will be seen that gray and purplish tones are about 
equally distributed through the conglomerate and that green is next 
in importance. The purplish colors are not confined to any particular 
part of the basin but are rather widely distributed. They are not: 
ordinarily intense; frequently they are only suggestions of the pur- 
plish or reddish tones. They are most strongly marked in some of 
the Nantasket ledges where they seem to be directly related to some 
of the effusive rocks of that region. 
——:—Bedding. It has been shown above that the pebbles and 
matrix of the conglomerate show little definite arrangement. Occa- 
sionally streaks or zones of finer material may be recognized in the 
hand specimen. The larger features of bedding are reserved for the 
next chapter. 
——:—Relations to Melaphyr. At several localities, notably on the 
southwest side of Walnut Hill and on the south side of Holyhood Cem- 
etery on Hammond Street in Brookline, at Newton Upper Falls north 
of the Reservoir on the west bank of the Charles River and in the Ar- 
nold Arboretum the conglomerate is locally and irregularly impreg- 
nated with basic lava. Some of these localities are apparently remote 
from known outcrops of melaphyr, but others are near large masses of 
that rock, the only igneous rock of the region. It seems probable, 
therefore, that these impregnations represent melaphyr. In hand speci- 
mens the lava shows flow structure parallel to the contact with the con- 
glomerate, and a finer grained darker zone immediately at the contact. 
Some of the pebbles of the conglomerate are enveloped and isolated 
by the lava. Under the microscope the igneous rock appears in 
tongues of partly devitrified basic glass containing magnetite in abun- 
dance and some well defined feldspar laths. There is some alteration 
