85 
granite is chiefly rounded, but some blocks, like many of the 
melaphyr fragments, are rather angular. The segregations of 
red jasper occur in all parts of the conglomerate, but most abun- 
dantly in the lower part. In none of the Nantasket rocks is it 
more plentiful or more favorably exposed for observation. In- 
terealated layers of sandstone show that the conglomerate is 
nearly horizontal, but undulating, along the north side of the 
hill; while around the western end the contact with the mela- 
phyr, and the strings of sandstone, dip gently (5°-10") to the 
east. The true thickness of the conglomerate is probably not 
over 25 feet and almost certainly less than the same bed on 
East Porphyrite Hill. The outlying ledge of conglomerate 
west of Granite Point, instead of belonging to the basal con- 
glomerate, as one might have judged from its position, is pre- 
cisely like the conglomerate of West Porphyrite Hill, being 
coarse and largely made up of.the underlying melaphyr, and 
containing numerous large fragments of granite, ete. The 
channel between this conglomerate and the ledges of melaphyr 
north of it probably marks a slight fault (10 to 20 feet) with 
the downthrow to the south. 
The overlying porphyrite, of which about 25 feet in thick- 
ness still remain, is very similar to the lower half of that on 
East Porphyrite Hill. It is compact (felsitic), not distinctly 
crystalline, porphyritic or amygdaloidal, and quite homogeneous 
except for the scattering and mostly small segregations of red 
Jasper. The colors are chiefly pale green and red tints, weath- 
ering usually light pink. The absence of the dark red variety 
which is so prominent on East Porphyrite Hill is due to erosion, 
the entire upper half of the porphyrite having been removed 
from the western hill, while the eastern hill still shows a com- 
plete section of the flow. The porphyrite is seen near the con- 
glomerate at several points on the north and west sides ; but the 
only clear and satisfactory exposure of the actual contact is 
afforded by the rather precipitous eastern face of the hill. 
The contact here shows an exceptionally steep southerly dip 
