198 C. D. WALCOTT — INTRA-FOKMATIONAL CONGLOMERATES. 



deposited in the intervening depressions beneath the sea. In the case of 

 the conglomerates of the Wilhite slates of Tennessee it is exceptional to 

 find a bedded limestone above them ; but within the Lower Cambrian 

 of Pennsylvania and Ncav York the conglomerates are interbedded in 

 the limestones. 



Large bowlders of limestone were observed in the Wilhite slates on 

 Wilhite creek, Tennessee, above the main conglomerate bed, and large 

 bowlders of limestone were observed in the bedded limestones at Stoner's 

 quarry, Pennsylvania. The mode of occurrence of these bowlders, 

 especially those in the limestones at Stoner's quarry, leads to the view 

 that they may have been dropped upon the sea-bed from floating ice. 

 No other explanation occurs to me that will account for the transporta- 

 tion of a bowlder from the shoreline and the placing of it upon the sea- 

 bed so as not to disturb to any marked degree the sediment then 

 accumulating. In the special example at Stoner's quarry two feet of 

 calcareous mud was deposited in thin layers about the bowlder and as 

 much more above it before the introduction of conditions that deposited 

 the next stratum of conglomerate.* 



The history of Appalachian sedimentation and mountain-building 

 proves that a more or less constant movement was taking place from 

 Algonkian time to the close of the Paleozoic. This movement was at 

 times greatly prolonged and resulted in marked topographic features. 

 More frequently the minor movements produced local effects, and some 

 of them resulted in the formation of the conglomerates described. 



* Sir William Dawson says that the " only means of explaining these conglomerates [Quebec, 

 Point Levis, Metis] seems to be the action of coast ice, which at this period appears to have been 

 as energetic on the American shores as at the present day, and seems to have had great reefs of 

 limestone, probably in the area of the gulf of Saint Lawrence, to act upon and to remove in large 

 slabs and bowlders, piling these up on banks to constitute masses of conglomerate." Quart. Jour,. 

 Geol. Soc, London, November, 1888, pp. 809, 810. 



