WILSON: MEDFOHl) DIKE AKEA. 
1 , JJirection of the ice movement. — The topography has been 
I described thus in detail, because there is a distinct relation between 
I the topography and the glaciation. The topography of the valley 
i to the west of Pine hill, which marks the location of the diabase 
ft dike, first drew the writer’s attention to the glaciation. The asym- 
1 metry of this valley is very noticeable, the eastern slope being 
I relatively gentle, while the w^estern is marked by nearly vertical 
I walls produced by the plucking action of the ice. (Fig. 1, i-n.) The 
I general slopes are such as to indicate that the motion was not trans- 
I ' verse to Pine hill ridge, nor yet parallel to it, but rather obliquely 
ft. across it, trending toward the south. These first observations as to 
I the direction of the ice movement in the valley were subsequently 
confirmed by the finding of glacial striae in two localities near the 
summit of Pine hill. 
Mr. Warren Upham states (’ 92 , p. 32) that the prevailing course 
of the glacial striae in Somerville is between S. 20° E. and S. 30° 
‘ E. At the Powder House dike, a southward extension of the Med- 
. ford diabase into the slates of the basin, the average direction of the 
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striae is about S. 34° E., being nearly transverse to the ridge. In 
the city of Medford, at the summit of Pasture hill there is one large 
exposure with an area of over four hundred square feet of almost 
^ fresh rock, quite hard and well glaciated, the striae running S. 30° 
J E. Further north, where the hill falls away, the striae vary slightly 
I to S. 39° E., the direction evidently being controlled by the topog 
•; raphy. At the Cedar Cliff road there are a number of well 
[ marked striae striking S. 37° E. From this point northward until 
P the Fells boundarv is reached, no well marked striations could be 
I found, the diabase being for the most part soil-covered, or, where 
B uncovered, the striae are too obscure to be noted. The same remark 
I applies to the striae on the glaciated surfaces of the granitic and 
I felsitic areas. A short distance north of the Fells boundarv and 
W ‘ before Pine hill is reached, striae trendino; S. 22° E. are found bv 
the roadside. At Pine hill just at the brink of the Big Quarry the 
striae trend 8. 21° E., the exposed surface upon which they appear 
dipping twenty-two degrees towards the northwest, so that the ice 
was evidently ascending. On the summit of the hill and a little 
further to the north, striae trending 8. 26° E. occur on a small dike 
cutting the felsite. On the west shore of Wright’s pond they trend 
8. 28° E., and five hundred yards further north some obscure 
grooves trend about 8. 22° E. 
