CAMBKIAN AND LOWER OEDOVICIAN. 135 



The next epoch probably began in Cambrian time with the deposition upon the ocean 

 bottom of muds and impure sands that are now represented by the Islesboro slate, with which 

 the Calderwood slate is possibly to be correlated. This deposition presumably took place in 

 moderately shallow water and not far from shore, but the position of the land masses which 

 furnished the sediments is whoUy conjectural. Gradually conditions became favorable for 

 the deposition of the beds now represented by the Coombs limestone. The considerable 

 amount of argillaceous material associated with the limestone, as weU as the great variations 

 in the purity of the limestone from place to place, may be taken as indicating shallow water 

 and somewhat shifting currents. 



The changes which closed the period of limestone deposition were more rapid and of greater 

 magnitude than those at its beginning and resulted in the deposition above the limestone of 

 sands and gravels of considerable purity which are now consohdated to form the Battle quartz- 

 ite. The conglomerate beds of this quartzite show a somewhat impure quartzitic matrix in 

 which are embedded pebbles of very pure quartzite. The fact that most of these pebbles are 

 well rounded indicates that the rock from which they were derived was itself a weU-indurated 

 sandstone or possibly a quartzite. The massive quartzites have a composition about Hke that 

 of the matrix in the conglomerates. Presumably these rocks represent shallow water or beach 

 deposits which were subject to the sorting action of waves and currents. No quartzite beds 

 which could have served as the source for such deposits are known in this part of the State, 

 though they may occur buried beneath later formations. 



The parent formation need not have been wholly or even largely of quartzite, for the 

 assorting and disintegrating action of waves and currents would suffice to separate more resist- 

 ant quartzitic portions from less resistant shaly or calcareous materials. Certain beds, however, 

 must have been very pure quartzite in order to furnish the clean, pure pebbles characteristic 

 of the conglomerate. 



After the deposition of the Battle sands and gravels conditions for the deposition of muds 

 were again restored and very extensive deposits were laid down, which are now represented 

 by the Penobscot slate, the most widely outcropping and the thickest formation of the region. 

 The change is probably indicative of shght but long-continued subsidence. Within the adjoin- 

 ing Rockland quadrangle these muds were succeeded conformably by thick deposits of limestone, 

 which is now thoroughly crystalline and of great economic importance in the production of 

 lime. The presence of beds of limestone conglomerate at various horizons within this limestone 

 formation indicates a shallow-water origin. 



Detailed descriptions of the formations are given in the Penobscot Bay folio. 



L 19. CABLETON AND YORK COUNTIES, NEW BRUNSWICK. 



The " slate belt" of southwestern New Brunswick comprises " Cambro-Silurian" 

 (that is, Cambrian and Ordovician) and Silurian ("Upper Silurian") strata, which 

 are separated by a marked unconformity and are intruded by granite. Bailey*** 

 states the conditions and exact localities of the observations made in 1900 and 

 concludes in part as follows : 



The general tendency of these observations has been to confirm the view * * * ^j^^^ 

 while a Silurian age must be assigned to certain tracts, such as that in which fossils were 

 found by Mr. Wilson, of the Geological Survej" staff, 6 miles north of Canterbury, and that 

 discovered by the writer in the settlement of Waterville, in the parish of Southampton, yet 

 the great bulk of the strata in the counties under consideration is, as previously supposed, of 

 greater antiquity, being at least Cambro-SUurian or Ordovician (the age to which they had 

 previously been assigned) , if not even older. In seeking for evidence on this question a careful 

 resurvey was made along the line where the supposed Cambro-Silurian or older rocks are met 

 and overlapped by the f ossihferous Silurian rocks to the north, with the result that incontestible 



