4 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 57 



In a word, the thought is that the Algonkian period, with its 

 great epicontinental formations, was a period of continental eleva- 

 tion and largely terrigenous sedimentation in non-marine bodies of 

 water, also a period of deposition by aerial and stream processes over 

 considerable areas. 



The recent map of the pre-Cambrian rocks of North America by 

 Van Hise and Leith [1909, pi. i] shows that the distribution of the 

 Algonkian rocks is confined to areas well within the margins of the 

 continental platform. The strata we have to consider on this map 

 are in the areas placed under the Algonkian, including Keewatin 

 areas in Canada and the Lake Superior region. Van Hise and Leith 

 [1909, p. 21] define the Algonkian as including "the major part 

 of the pre-Cambrian sedimentary rocks, though it also contains sedi- 

 ments so deformed and metamorphosed that their stratigraphy cannot 

 be deciphered. The Archean is the basement complex, perhaps in- 

 cluding several series or groups upon which the Algonkian rests, so 

 far as known, with unconformity." 



The sediments of other Algonkian areas of North America were 

 much like those of the Lake Superior region in having immense 

 quantities of sand and mud. and, more rarely, great thicknesses of 

 calcareous matter.' 



Briefiy, the rocks of the later Algonkian formations may be out- 

 lined as follows : 



Western North America 

 Grand Canyon series, Arizona. [Walcott, 1899, PP- 215-216.] 



FEET 



Chuar terrane (composed of fine-grained sandstone, argillaceous 



and arenaceous shales, and 285 feet in thickness of limestone) 5,120 



Unkar terrane (composed mainly of sandstones with a bed of 

 magnesian limestone 150 feet in thickness and a series of 

 basalt flows 800 feet in thickness 6,830 



Total thickness 11,950 



There are no conglomerates except a bed not exceeding 30 feet 

 in thickness at the base. 



The Llano series of Texas is much like the Grand Canyon series 

 [Walcott, 1884, pp. 431, 432]. 



The Belt series of Montana [Walcott, 1899, pp. 201-209; 1906, pp. 

 2-15, 17-21] and British Columbia, Canada [Walcott, 1906, pp. 21- 



^ For data relating to the description of the Algonkian rocks see Van Hise 

 and Leith, Bull. No. 360, U. S. Geol. Survey. 



