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the Paradoxides slates, subsequently to the eruj)ti()n through 

 them in succession ot" the granitic rocks, — diorite, granite, and 

 t'elsite, — and subsequently to the extensive erosion which has so 

 largely swept away these ancient sediments, began the pro- 

 gressive subsidence, accompanied in its earlier stages by 

 volcanic activity, during which were formed the conglomerate 

 and interbedded lavas of the Nantasket area. Oidy the latest 

 bed of lava poured out in this part of the basin is exposed in 

 Hingham, west of Rocky Neck ; but the cessation of the 

 igneous outbursts was followed by the great conglomerate 

 series of Hingham, with its interstratified beds of sandstone 

 and slate ; and the variable character of the strata is a plain 

 indication that the [)hysical conditions were far from uniform 

 during this period. The conglomerate occiu's mainly in beds 

 from twenty to eiglity feet thick alternating with, usually, 

 thinner beds of gray sandstone and red or gray slate, for a 

 total thickness of nearly one thousand feet. In fact, no other 

 part of the Boston IJasin affords such clear and abundant evi- 

 dence of: (1) frequent changes from beach or shallow water 

 deposits (conglomerate and sandstone) to those formed in 

 deep and quiet water (slate), and vice vers<i; and (2) the 

 oscillations of the earth's crust, upon which these changes 

 usually depend. This intermittent conglomerate series appears 

 to pass somewhat gradually and with perfect conformity up 

 into the great slate series, which consists throughout of a fine, 

 dark gi*ay slate, and has an apparent thickness of at least one 

 thousand feet, without any interstratified beds of coarser 

 material. This is sufficient to prove that the oscillations of 

 level attending the formation of the conglomerate series were 

 followed by a profound and prolonged subsidence ; for during 

 all the time when the slate was being slowly and quietly depos- 

 ited, Hingham must have formed the floor of a comparatively 

 deep ocean. But this tranquility could not hist forever ; for 

 the subterranean forces were slowly gathering strength, and 

 the formation of the slate was undoubtedly terminated by the 



