3()2 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
granite ridge, with here and there vertical faces towards the east 
and gentle slopes and soil-covered surfaces on the west, marking the 
western boundary of the dike ; on the right, the land at first slopes 
very abruptly to about the level of Hall road, but further north the 
grade gradually becomes less steep. 
Proceeding from here northeastward along the line of the dike, 
the surface is gentlv undulating with obscure ridges trending south- 
east, and almost completely soil-covered. To the east, granitic 
ridges stand out above the general level of the dike, and valleys 
between them are depressed below this level. At the boundary of 
the Middlesex Fells there is a depression on the east, a quick rise to 
the level of the diabase, and then a second abrupt rise marking the 
western boundary of the dike, and from here a gentle downward 
slope. 
Passing up Owen’s walk, which i*uns along the middle of the 
dike, with Pine hill on the right and a much lower ridge on the left, 
the dissimilarity of the slopes on right and left is very conspicuous. 
On the right the slope to the summit of Pine hill is gradual, while 
on the left there is a nearly perpendicular wall of varying height, 
and a steep talus slope at its base. Pine hill rises two hundred and 
fifty feet above sea level, with its summit one hundred and seventy 
feet above the valley on the east. The eastern face of the hill is, 
for the greater part of its length, a cliff varying in height up to 
about seventy feet, with an exceedingly steep talus slope made up 
of fairly large angular blocks at its base, grading into finer materials 
as the distance from the base of the cliff increases. The eastern or 
opposite side of the valley presents a much more evenly graded 
slope than is found on the western Hank of Pine hill. This east¬ 
ern valley is also much wider and deeper than the dike ” valley, 
and extends northeastward about two miles. 
North of the elbow of Owen’s walk, where it bends to join Forest 
street, the ridge on the left presents to the eastward an almost verti¬ 
cal face nearly sixty feet in height (Fig. 1, i). After crossing the 
width of the diabase there is a slight elevation and then a gradual 
descent into the valley which lies to the east of Pine hill. 
The diabase dike at its extreme northern end, beyond Pine hill,, 
becomes narrowed to a width of fifty feet, and is marked on both 
sides by vertical walls of granite here six or eight feet in height, 
ending in an area now occupied by a swamp which marks the 
granite-felsite contact. 
