TEE CAUSE OF TEE GLACIAL PERIOD. 487 



made may not have originated in the near vicinity, and so 

 their subangular condition need not imply glacial agency in 

 transportation. 



Professor Shaler also is inclined to attribute the exten- 

 sive conglomerate deposits of the Carboniferous age in the 

 Appalachian district of North America to glacial action ; 

 and certainly the extent of these conglomerate deposits un- 

 derlying the coal-beds is surprising. " In Pennsylvania they 

 are about one thousand feet ; in eastern Kentucky and east 

 Tennessee their thickness rises to about two thousand feet. 1 ' 

 Similar conglomerate deposits everywhere underlie the Car- 

 boniferous system. According to Professor Shaler, " we 

 find it from southern France to Scotland, from Alabama to 

 New Brunswick, in India, and elsewhere." For the most 

 part, however, the pebbles of this conglomerate consist of 

 quartz or quartzite, well rounded, and seldom of larger size 

 than can readily be transported by water ; though Professor 

 Newberry is reported to have " found a bowlder of quartz- 

 ite seventeen inches by twelve inches, imbedded in a seam 

 of coal." Altogether it seems more likely that we have in 

 these conglomerates underlying the Appalachian coal-fields 

 of America the wash brought down by large rivers heading 

 in the mountain plateau toward the north and east, of which 

 the Archaean range on the Atlantic border, together with the 

 hills of New England and the Adirondacks of New York, are 

 but the remnants. That floating ice may have played some 

 part in the streams coming down from these mountain-heights 

 is not improbable ; but it is doubtful whether the facts war- 

 rant us in inferring anything more. 



Professor Shaler would also attribute a still lower series 

 of conglomerates whose typical development is in eastern 

 Tennessee and western North Carolina, and which rests un- 

 conformably upon Lauren tian rocks, to glacial action ; though 

 he confesses that no scratched bowlders have yet been dis- 

 covered in these deposits, but he writes : u Recollecting that 

 we know of no force that is competent to bring together such 

 masses of pebbles derived from a wide-spread surface save 



