NO. I ABRUPT APPEARANCE OF THE CAMBRIAN FAUNA 9 



Doctor Barren's view that the Hmestones are of marine origin is 

 similar to the one that largely influenced me in the past to consider 

 that the Grand Canyon and similar series of Algonkian formations 

 were of marine origin. 



PRE-CAMBRIAN CONTINENTAL SURFACE 



In 1892 I published the opinion that the North American con- 

 tinent 



Was larger at the beginning of Cambrian time than dnring any epoch of 

 Paleozoic time and probably not until the development of the great fresh- 

 water lakes of the lower Mesozoic was there such a broad expanse of land 

 upon the continental platform between the .Atlantic and Pacific oceans. 



The continent was well outlined at the beginning of Cambrian time ; and I 

 strongly suspect, from the distribution of the Cambrian faunas upon the 

 Atlantic coast, that ridges and barriers of the Algonkian continent rose above 

 the sea, within the boundary of the continental plateau, that are now buried 

 beneath the waters of the Atlantic. On the east and west of the continental 

 area the pre-Cambrian land formed the mountain region, and over the interior 

 a plateau existed that at the beginning of, or a little before. Upper Cambrian 

 time was much as it is to-day. Subsequent mountain building has added to 

 the bordering mountain ranges, but I doubt if the present ranges are as great 

 as those of pre-Cambrian time that are now known only by more or less of 

 their truncated bases. The Interior Continental area was outlined then and 

 it has not changed materially since. Its foundations were built in Algonkian 

 time on the Archean basement, and an immense period of continent growth 

 and erosion elapsed before the first sand of Cambrian time was settled in its 

 bed above them. [Walcott, 1892, pp. 562-563.] 



When the Californian Cambrian sea began its invasion of the 

 Algonkian land in southwestern California and Nevada there awaited 

 the incoming waters a land surface deeply disintegrated and more 

 or less base-leveled by erosion. As compared with the earlier epoch 

 of the Algonkian it was a featureless continent, the elevations caused 

 by folding and uplift in the geosynclines of the Cordilleran, Lake 

 Superior, and Appalachian areas having been largely degraded. The 

 rising waters of the Cambrian sea met with few marked elevations 

 in the Cordilleran and Appalachian troughs, as is evidenced by the 

 absence of coarse conglomerates and the presence above the basal 

 conglomerates of immense deposits of very fine sandstone and mud 

 rocks in the Lower Cambrian. 



The character of the pre-Cambrian surface in the southern Appa- 

 lachian area is well indicated in the description by ^Ir. Arthur Keith, 



