Dodge.] 408 [February 3, 



While these conglomerates often show no marks of stratification, 

 elsewhere they pass into sandstones and slates. And these latter so 

 much resemble, at times, the slates already described, as to make great 

 uncertainty as to whether they are really different formations. Thus, 

 in Newton, it cannot be determined always whether the frequent 

 slate outcrops are of the Cambridge variety, or connected with the 

 conglomerates. Some of them certainly pass into the conglomerates, 

 while others, though very similar in position and character, seem to 

 belong to the other group. 



The passage of conglomerates and slates into each other at Chest- 

 nut Hill Reservoir has been described by Prof. Shaler. 1 The slates 

 are sometimes very thin, and often curved. A locality about a mile 

 west, on the north side of Beacon Street, was exposed in the spring 

 of 1874 by the work of tunnelling the rock to make the connection 

 of the reservoir with Sudbury River. Here, conglomerate at the 

 bottom passes to slate in a section well exhibited by a high wall of 

 rock close to the road. 



The rippled slates or sandstones in Brighton, south of Cambridge 

 Street, west of Warren, and between Warren and Allston Streets, of 

 course show formation in shallow water. 



South of a line from the southern corner of Newton across Brook 

 Farm, south of Weld Street, across Forest Hills Cemetery, and turn- 

 ing more to the northward at Dorchester line, yet including Savin 

 Hill, the conglomerate disappears, giving place to the slate (b) above 

 noticed. On this line, there is a passage of conglomerate to slate 

 and sandstone, at the west side of Morton Street, north of Canter- 

 bury Street in West Roxbury, where the rock has been quarried, and 

 still forms a high wall showing a high dip southward. A little south, 

 there is a passage of conglomerate to slate, probably a part of the 

 same series. Again at the southern corner of Washington Street 

 and the New York and New England Railroad in Dorchester, the pas- 

 sage can be detected in the unbroken ledges. Erratics of the brown 

 sandstone to which the larger conglomerate gives place, may be seen 

 on Commercial Point. 



Although there is perhaps nothing in the apparent lack of stratifi- 

 cation in a large portion of the conglomerates inconsistent with their 

 accumulation at a beach, (this being a common occurrence with ac- 

 cumulations of coarse pebbles) , this feature accords better with the 

 requirements of the theory of their glacial origin. I need hardly 



1 Proc. Boat. Soc. Nat. Hist. (1869), Vol. xin, p. 176. 



