217 , 



which marks the position of another main axis of depression ; 

 but it also includes a narrow and much-faulted syncline. 



In Hyde Park and the north-east corner of Dedham the 

 pudding-stone lies irregularly among and upon the crystallines, 

 usually dipping away from the latter at low angles. I have 

 recently observed ledges of Huronian petrosilex and Shaw- 

 mut breccia between the Boston and Providence and New 

 York and New England Railroads, a few rods north of the Read- 

 ville Station, and within the area mapped as wholly composed 

 of conglomerate. These ledges are. probably a continuation of 

 the axis of older rocks marked as extending over Fairmount 

 and Brush Hill into Milton. At some points the conglomerate 

 can be observed in close proximity to the Shawmut breccia 

 and brecciated petrosilex (see ante, p. 175), but it is seldom 

 difficult to distingush the different formations . This conglom- 

 erate occasionally passes into arenaceous beds, but I have 

 observed no true slate in Hyde Park. Between the elongated 

 area of petrosilex and amygdaloid already described, crossing 

 Blue Hill Avenue, in Milton, and the petrosilex and breccia 

 north of the Neponset, the conglomerate undoubtedly forms a 

 synclinal. Farther east this broadens, and is divided by the 

 other island of ancient rocks south of the river, between Matta- 

 pan and Milton Lower Mills, into an anticlinal and synclinal ; so 

 that, including the conglomerate on the north of the breccia, in 

 Dorchester, this part of the Hyde Park and Squantum conglom- 

 erate belt, which is here one and a half miles broad, forms two 

 anticlinals and a synclinal ; the crests of the former having been 

 removed, exposing broad bands of the underlying crystallines. 

 Occasional isolated patches of the conglomerate scattered over 

 these crystalline areas prove the former continuity of this rock. 

 In this part of its course the synclinal begins to include some 

 slate ; and a generalized north-south section from Pine Tree 

 Brook to the broad band of slate in Dorchester is represented 

 by PI. 4, fig. 6. 



The slate in this narrow or Neponset synclinal is not con- 

 tinuous along the strike, but the evidence is plain that the 



