227 



quite like sandstone. Strike, N. 80° E. ; dip, vertical ; thick- 

 ness exposed, traverse measure, probably three hundred feet. 

 These are beds of passage, and serve to locate with exactness 

 the boundary between the two terranes at this point. There 

 are no other outcrops on this line of strike, either to the east or 

 west. On the map the northern boundary of the slate band is 

 carried too far to the north at the east end, a line bisecting 

 Commercial Point probably coming nearer the truth. The 

 gradual passage from the slate to the conglomerate on the 

 south side of the synclinal is well exposed in Mount Hope and 

 Mount Calvary Cemeteries, as already noticed. 



North of this West Roxbury and Dorchester slate belt the 

 conglomerate maintains a high southerly dip for a considerable 

 distance, giving for this rock, as for the slate, a great apparent 

 thickness. In this instance, however, we have satisfactory 

 evidence of strike faults, with the upthrow on the south, aug- 

 menting the apparent volume of the strata. In West Roxbury, 

 at most points along a line about one-half mile north of the 

 slates, the country rises abruptly; the uplift forming, for con- 

 siderable distances, a nearly continuous line of escarpment facing 

 the south, a prominent feature in the topography of the region. 

 It is less distinct through Dorchester ; but the abrupt southern 

 slope of Savin Hill is about on this line, and serves to locate the 

 eastern end of the break. The narrow belt between this topo- 

 graphic uplift and the slate band affords several interesting north- 

 south sections ; the best, however, is that exposed on the line of 

 Morton Street, near Forest Hills Cemetery. The escarpment, 

 which is well-marked here, is backed by conglomerate ; and this 

 changes on the face of the cliff, as it were, through grits to sand- 

 stone. The dip is south 70°. After perhaps four hundred feet 

 concealed, there are whitish slates, ripple-marked and dipping 

 S. 75° ; and, a few rods beyond these, conglomerate passing into 

 soft, light -colored slates, with a southerly dip of 80°. Several 

 hundred feet farther south, just across Canterbury Street, the con- 

 glomerate reappears with a high southerly dip, and probably con- 

 tinues without interruption to the main band of slates. Although 



