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much obscured in this part of its course, and farther west, by 

 large drift hills on the south. On Centre Street, near Weld, 

 there is a compact gray slate with conglomerate toward the south. 

 I have seen no slate west of this, but conglomerate, arenaceous 

 and slaty, and with a high southerly clip, occurs on South 

 Street, near TV eld Street, and on Maple Street, between Weld 

 and Centre Streets. West of the point last named there are 

 no outcrops. For convenience' sake the slates of the narrow 

 belt of variable lithological character just described, which are 

 considered, for the most part at least, as detached strips of the 

 main band of slate on the south, have not been separately rep- 

 resented on the map, but are included with the conglomerate. 



The Broolcline and Roxhury Oonglomerate Belt. — We 

 are now on the southern border of the largest mass of con- 

 glomerate in the Boston basin, a band averaging nearly three 

 miles wide and covering not less than twenty square miles. 

 It is split along the middle, for a distance of four miles 

 from the western end, by the great mass of amygdaloid in the 

 south part of Newton and the adjacent portion of Brookline. 

 North of the Forest Hills and Savin Hill escarpment slaty and 

 sandy beds are almost entirely wanting in this area ; the rock 

 is mainly large-pebbled ; and, although over a large part of the 

 belt the ledges are very prominently placed, giving rise to the 

 most picturesque scenery of this region, and aiFording magnifi- 

 cent exposures, there are comparatively few points where 

 satisfactory observations of the dip can be made. 



The straight, smooth slopes of rock, and the narrow, 

 vertical-walled defiles so characteristic of this conglomerate, 

 originate mainly in the larger joints of the rock. These planes 

 of division are found in all the conglomerate of this region, but 

 have their best development in the area in question, where 

 their striking characters have attracted the attention of all 

 observers. Many of these master joints have approximately 

 east-west trends, producing ridges and escarpments substantially 

 parallel with the strike of the rock ; and another well-marked 

 set cuts the beds in the direction of the dip. Wherever the 



