Schuchert— Cambrian of ike Grand Canyon of Arizona. 363 



Cambrian of Arizona appear to have come from the east 

 (New Mexico, etc.) and from- the south and southeast 

 (Mexico). As the epeiric sea advanced over the ancient 

 peneplain, it first gathered into the basal member of the 

 Middle Cambrian the old regolith which lay on the plain 

 and which was essentially one of quartz sands and peb- 

 bles. Succeeding this introductory deposit, the rivers 

 brought at first much mud and less fine sand, and finally 

 less and less of muds and the finest of sands but more and 

 more of solution materials. From this we learn that the 

 lands furnishing the sediments were low and that the 

 rivers probably were more or less long, for they brought 

 only finer sediments and solution materials. Through- 

 out Cambrian time none of the lands to the east and 

 southeast of the Grand Canyon area appear to have 

 undergone crustal movement other than warping. To 

 the west of the Cordilleran geosyncline the story is a 

 different one, but as it is outside of our area of descrip- 

 tion and did not furnish sediments to it, it need not be 

 considered. 



Contact with the Vishnu. — The contact between the 

 Cambrian and the Archean is to be seen very clearly on 

 Hermit Creek just below the camp site (see figs. 4 and 5). 

 The Archean gneiss is much folded and contorted and the 

 planes of gneissoid banding appear to dip nearly verti- 

 cally. The gneiss is cut by dikes of pegmatite and by 

 large bodies of granite. On these ancient rocks rests 

 the Cambrian series in nearly horizontal strata, and the 

 sea invaded the land over an almost plane surface. In 

 a distance of several hundred feet the plane of the trans- 

 gressing sea does not have hollows in it of more than 

 3 feet (fig. 5). In a long distance view, however, one 

 can see places where the Vishnu rises sharply above the 

 peneplain and seemingly sometimes several hundred feet. 

 These monadnocks made islands in the sea of earlier Mid- 

 dle Cambrian time. Elsewhere this peneplain as it 

 extends over the Proterozoic strata (Grand Canyon 

 series) also has its monadnocks and ridges of quartzites 

 trending northwest and southeast, and they protrude 

 even higher into the Cambrian than do those of the 

 Vishnu, up to 700 feet Noble 1 describes this peneplain 

 as follows : 



l L. F. Noble, this Journal, (4), vol. 29, p. 527, 1910. 



