188 A. P. COLEMAN DRY LAND IN GEOLOGY 



stone in Ontario, and under Silurian, Devonian, and Cretaceous rocks 

 toward the southwest. How far the unchanged pre-Huronian peneplain 

 or its little changed successor extends south westward beneath the strati- 

 fied rocks is unknown. 



Much of this vast surface has been buried at one time or another and 

 sheltered from erosion by marine sediments, and has since been disin- 

 terred scarcely modified; but it is probable that it was never all covered 

 by the sea at once. Portions of it seem to have remained dry land as 

 cities of refuge for the inhabitants in every inundation. 



That other continental nuclei have had similar histories may be con- 

 sidered certain. In Scotland and Scandinavia nearly horizontal Precam- 

 brian beds, whether of glacial origin or not, cover a peneplain closely 

 like ours; and quartzites and conglomerates called Precambrian may be 

 seen resting with gentle clips on a similarly truncated plain in West Aus- 

 tralia. Near Clackline, for instance, Huronian-looking quartzite rests on 

 gneiss penetrated by pegmatite dikes ; and at several places in the neigh- 

 borhood of Kalgourlie and Koolgardie a somewhat tilted conglomerate, 

 like that of the American Huronian, overlies the steeply clipping gneissoid 

 rocks. 



Pre-Huronian Land Conditions 



No unchanged land surface has yet been found below the peneplain 

 just described, but important land areas can be inferred with certainty, 

 though now obliterated by squeezing and folding and the metamorphism 

 due to eruptive granites. The great development of clastic sedimentary 

 rocks included under the names Seine Series, Sudbury Series, Temis- 

 caming Series, etcetera, widely distributed over the Canadian Shield, 

 imply broad lands and even mountain ranges far older than those de- 

 stroyed before the Huronian. 



They generally begin with a great basal conglomerate, so coarse and 

 bouldery sometimes as to suggest ice-action, but squeezed and rolled out 

 and folded in with other rocks in ways that make the finding of striated 

 stones or a striated surface beneath quite hopeless. It is, however, highly 

 probable that the climate was, in general, cool and moist, for the rocks 

 are gray and often include arkoses with little weathered feldspars, though 

 Lawson speaks of the Seine conglomerate in one place as a "fanglom- 

 erate" of desert formation. The rocks as a whole suggest a continental 

 origin and their materials must have come from the weathering of land 

 surfaces. Some of the graywackes and slates are very evenly bedded and 

 show regular alternations of coarser and finer materials caused by vary- 

 ing seasons, either warm and cold or wet and dry. They resemble the 

 stratified silt and clav laid down in glacial lakes at the end of the Pleis- 



