1884.] 13 [Crosby. 



erate and slate is shown, not only by a general agreement in 

 strike and dip, but also by the phenomenon observable at many 

 points of a gradual lithologic passage between them. As a rule, 

 the portions of the conglomerate showing the maximum of coarse- 

 ness and irregularity are those in immediate contact with the 

 underlying crystalline rocks. Here the conglomerate is some- 

 times a genuine breccia and often holds fragments or boulders of 

 large size. Passing upward, this gives way to the more normal 

 and common type of conglomerate, the true puddingstone, in 

 which the pebbles rarely exceed six inches in diameter and are 

 well rounded. Still higher, limited beds and patches of grit and 

 sandstone are intercalated, and these appear more frequently as 

 the pebbles become smaller, finally including layers of [slate ; and 

 thus the formation is gradually changed from a coarse conglom- 

 erate to an impalpable slate. From the earliest conglomerate to 

 the latest slate the deposition has evidently been substantially 

 uninterrupted, and has gone on during a period of subsidence 

 with which the growth of the deposits did not keep pace. 



Indications of this gradual passage between the conglomerate 

 and slate may be observed at most j^oints where there are out- 

 crops along their mutual boundaries. But it is, perhaps, best dis- 

 played at the following localities : At several places in Hing- 

 ham; on the Old Colony Railroad between the Wollaston and 

 Quincy Stations, and along Black's Creek one-fourth mile west 

 of the railroad; near the New York and New England Railroad 

 in Mattapan ; North Quincy, one-half mile northeast of Atlantic 

 Station ; the shore on the outer end of Squantum ; Mt. Hope 

 Cemetery; between Florence Street and Hyde Park Avenue, 

 near Mt. Hope Station ; Newton Centre ; Newton Upper Falls ; 

 Newton Corner; and in the neighborhood of Grantville and of 

 South Natick. 



The statement has been made that the slate as a whole is char- 

 acterized by steeper dips than the conglomerate. But I have not 

 been able to verify this observation. Both these rocks are, for 

 the most part, highly inclined, often vertical. In fact, they have 

 suffered an enormous amount of disturbance, chiefly in the form 

 of folds, faults and igneous intrusions; and, in consequence, 

 adjacent outcrops of conglomerate and slate sometimes show 

 very discordant dips. But the same sort of evidence would prove 



