225 



at the ledge one-fourth mile west of the railroad, the conglom- 

 erate is massive and the stratification obscure. The next and 

 last point where conglomerate crops on this line is a few rods 

 south-west of Beach Street, and nearly midway between Wash- 

 ington and Poplar Streets. It here very clearly forms an isolated 

 patch resting on the granite ; this is not indicated on the map. 

 Continuing on this line, the uncrystallines are concealed for 

 more than a mile ; and then slate appears in West Roxbury 

 Village quite near the granite, the conglomerate being probably 

 cut off by a fault. Large conglomerate boulders in the drift 

 indicate that this rock separates the granite and slate for a con- 

 siderable distance west of Washington Street, farther than 

 mapped, though finally disappearing before reaching the Ded- 

 ham Branch Railroad. 



The band of slates of which we have now reached the south- 

 ern border is the best defined and most uniform rock belt in 

 the Boston basin. It has a nearly constant breadth of about 

 five-eighths of a mile, and the dip of the slate is at most points 

 nearly or quite vertical ; while the strike ranges from E.— W. 

 to N. 70° E. This is a very homogeneous, and yet for the 

 most part distinctly stratified, grayish-black variety of slate ; the 

 bedding is usually very even, and free from contortions. The out- 

 crops are confined mainly to the middle portion of the belt ; the 

 land on this line, east of Dorchester Avenue and west of the 

 Dedham Branch Railroad, being mainly of drift formation ; 

 and the rock boundaries in these directions, as marked on the 

 map, are consequently somewhat hypothetical. The most west- 

 ern exposures are those on either side of the railroad and near 

 the granite in West Roxbury Village. The dip at this point is 

 southerly, but very variable, 50° to vertical. On the railroad, 

 at the Beach-Street crossing, and between Central Station and 

 Roslindale, the dip is S. 80°. This is near the northern border 

 of the belt. On Maple Street, south-west of Roslindale Station, 

 the strata are quite vertical. The next outcrops are those 

 already described in Mount Hope Cemetery, on the south side 

 of the belt ; and exposures occur on the same line in Madison 



OCCAS. PAPERS B. S. N. H. — III. 15 



