298 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 64 



10. ( Walcott) The evidence both direct and by deduction sustains 

 the view of a long- pre-Cambrian interval of erosion resulting in a 

 marked unconformity. The Algonkian in America consists of a 

 great series of epicontinental formations between the Archean and 

 Cambrian. The Rothpletz view of considering all of the pre-Cam- 

 brian sedimentary formations of North America corresponding to 

 the Belt series as of probable Cambrian age is without evidence to 

 support it. 



Some general conclusions. — {Walcott) It is unfortvmate that my 

 respected colleague in preparing his memoir should have failed to 

 fully examine literature on the subject available in the libraries of 

 Munich or to secure fuller information and maps from official sources 

 in this country. A request on his part for information as to what had 

 been published on the Helena district, sent either to the Director of the 

 U. S. Geological Survey or to me in the winter of 1913-1914, or while 

 he was at my camp on Burgess Pass, British Columbia, would have 

 informed him of the geologic map of the Helena District and descrip- 

 tions contained in Bulletin 527 of the Survey. 



In final conclusion let me add that there is a great amount of work 

 yet to be done on the pre-Cambrian sedimentary rocks of the North 

 American continent. Those of the Lake Superior region are largely 

 well mapped and described, as are portions of those of the Appa- 

 lachian region, central Texas, southwestern Colorado, and northern 

 Arizona, but large areas in Montana and northward in Alberta and 

 British Columbia remain to be studied, mapped, and described. New 

 discoveries will be made and older views changed, but in the light of 

 our present information I think we are forced to accept the evidence 

 that the Algonkian formations of North America are of pre-Cambian 

 age; of continental origin, and formed of terrigenous deposits that 

 accumulated on river flood-plains and other favorable areas, or de- 

 posited in epicontinental, brackish-water seas or fresh-water lakes 

 that filled depressions within the area of the Cordilleran and Appa- 

 lachian geosynclines ' and the Lake Superior region. 



^Problems of Geology, Yale Univ. Press, 1914, Chap. 4: The Cambrian and 

 its Problems, p. 165. 



