328 WALCOTT 



from a considerable distance, and from a source of supply 

 quite different from that which furnished the sands of the 

 Lower Cambrian and the sediments above the St. John quartz- 

 ite in the Middle Cambrian. 



Mr. Matthew's argument for the presence of a great uncon- 

 formity beneath the St. John quartzite was primarily based on 

 the variation in thickness of the strata of the Hanford ' Etche- 

 minian ' terrane. In the sections about St. John the St. John 

 quartzite sometimes rests on the pre-Paleozoic strata, and in 

 other localities a relatively thin section of the Hanford terrane 

 is intercalated. At Hanford Brook the Hanford terrane is more 

 than 1000 feet in thickness, while in the near-by Kennebecasis 

 valley it is entirely absent. Mr. Matthew conceived the view 

 that the non-presence of the Hanford ' Etcheminian ' terrane was 

 owing to its removal by erosion prior to the deposition of the St. 

 John quartzite. It may have been that when the Lower Cam- 

 brian sea began to deposit sediments in this region the topog- 

 raphy of the sea bottom was very irregular and that the sedi- 

 ments were deposited on an uneven surface of Algonkian rocks. 

 There does not seem to be any evidence of erosion, either in the 

 presence of debris in the basal beds of the St. John quartzite or 

 in an irregularly eroded surface of the Hanford terrane. On 

 the contrary, there is every evidence of the overlap of the various 

 beds of the Hanford terrane on the subjacent Algonkian rocks. 



From the character of the sediments of the Hanford series it 

 is evident that they were deposited on a gradually subsiding 

 surface. The lowest basal beds are conglomerates, followed 

 by finer sands, and again by beds of conglomerate and coarse 

 sandstones at intervals throughout the terrane. As the land 

 subsided the sediments gradually overlapped on the lower por- 

 tions of the topography, finally reaching a height of 1000 or 

 more feet above the horizon at which the basal beds were de- 

 posited. In shallow waters only a thin layer of the sediments ac- 

 cumulated. When the sands of the St. John quartzite were dis- 

 tributed over this series there may have been a slight erosion by 

 the currents distributing the sand, but there would not neces- 

 sarily be any marked unconformity between the two terranes. 



It seems to me that the view that the variation in thickness of 



