THE LA URENTIAN PENEPLAIN 667 



some such process of erosion as McGee describes under the title 

 of "Sheet flood erosion" (28). He describes the surface of a 

 portion of the subarid Sonora district in southern California as 

 being a plain cut on crystalline rocks, with little soil cover in situ. 

 In some features this plain resembles that of the Canadian pene- 

 plain, but it has relatively a very limited area. On the Canadian 

 peneplain, however, the basins as well as the ridges are free from 

 rock debris in situ. 



The normal processes of subaerial erosion or of marine ero- 

 sion do not seem competent to remove the material from the 

 basins as well as from the ridges ; and, in addition, they do not 

 produce residual land forms with surfaces so little decomposed 

 as are the crystalline surfaces everywhere. 



Alfred W. G. Wilson.' 

 McGiLL University, 

 Montreal, Canada, 



LITERATURE. 



1. Agassiz, Louis, 1849. "On the Origin of the Actual Outlines of Lake 



Superior." Proc. Amer. Soc. Adv. Sci., Vol. L 



2. , 1850, Lake Superior, Its Physical Character, Vegetatio7i and 



Animals (Boston), pp. 417-26. 



3. Back, Sir George, 1836. Narrative of the Arctic Land Expedition, 



in 1833-34-35. 



4. Barlow, Alfred E., 1899. "Report on the Geology and Natural 



Resources of the Area Included by the Nipissing and Temiscaming 

 Map Sheet, Comprising Portions of the District of Nipissing, Ontario, 

 and of the County of Pontiac, Quebec." Can. Geol. Surv., Vol. X, 

 new series, Report I. 



5. Bell, Robert, 1884. "Report on the Geology of the Northern Shore 



of Labrador." In Report of Hudson Bay Expeditiofi under Lieut. A. 

 R. Gordon. Dept. of Interior, Ottawa, Can. 



6. , 1885. "The Topography and Geology of the Hudson Bay 



Region." Science, Vol. I, pp. 256, 257. 



7. — , 1887. "Report on Explorations of Portions of the Attawa- 



pishkat and Albany Rivers, Lonely Lake to James Bay." Can. Geol. 

 Surv., Report for 1886, Part G. 



8. , 1894. Pre-Paleozoic Decay of Crystalline Rocks North of 



Lake Huron." Geol. Soc. Amer., Bull., Vol. V. pp. 357-66. 



9. Daly, R. A., 1902. "The Geology of the Northeast Coast of Labrador," 



Bidl. Mus. Comp. Zoo. (Cambridge), Vol. XXXVIII, pp. 205-70, 



