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Street, near Blue Hill Avenue. North of this, between the 

 avenue and the New York and New England Railroad, the slate 

 is exposed almost continuously for five hundred feet across the 

 strike, the dip ranging ten degrees either side of the vertical. 

 At the corner of Dorchester and Welles Avenues, slightly 

 arenaceous slate shows a southerly dip of 80°. This slate belt 

 outcrops for the last time east of Dorchester Avenue and south 

 of Centre Street ; but, if continued, it must underlie Thomp- 

 son's and Spectacle Islands. 



The position and structure of this band of slate are unquestion- 

 ably synclinal. I have already shown that the conglomerate on 

 the south side of the slate dips toward the latter, as if passing 

 beneath it. On the north side the relation is the same, the con- 

 glomerate masses showing a high dip to the south, or toward 

 the slate. This geological valley is well represented in the 

 modern topography, the low meadows along this belt being in 

 striking contrast with the broken conglomerate hills to the north 

 and south. As well remarked by Mr. Dodge, the Dedham 

 Branch Railroad turns aside to utilize the convenient course 

 which nature has provided. The form of the valley is obscured 

 at some points by drift hills, but the general course corresponds 

 with the strike of the slates and the trend of the belt. If we 

 regard this as a simple synclinal, free from faults, then the vol- 

 ume of slate involved can scarcely be less than fifteen hundred 

 feet. I have observed no reliable indications of dislocations, 

 but the slate is so homogeneous that fractures might easily 

 exist undetected. 



Toward the north, especially, there is an evident passage 

 from the slate to the conglomerate. This is seen most clearly 

 in the angle between Florence Street and Hyde Park Avenue, 

 just north of Mt. Hope Station on the Boston and Provi- 

 dence Railroad. The rock here is mainly a slaty conglomerate, 

 or rather a fissile slate with interspersed pebbles of small size ; 

 sometimes, however, approaching a normal pudding-stone, with 

 pebbles three to four inches in diameter. The pebbles are 

 mainly petrosilex, occasionally granite. Some of the beds are 



