362 Sehuchert — Cambrian of the Grand Canyon of Arizona 



Art. XXIII. — The Cambrian of the Grand Canyon of 

 Arizona; by Charles Schuchert. 



[Contributions from the Paleontological Laboratory, Peabody Museum, 

 Yale University, New Haven, Connecticut, U. S. A.] 



In the month of September, 1915, the writer had the 

 great advantage of spending four days studying the Cam- 

 brian of the Grand Canyon of Arizona in the vicinity of 

 El Tovar. One day was devoted to the Bright Angel 

 trail and the others to the depths of the canyon about 

 Hermit camp. The purpose of this article is not to 

 describe the Cambrian of this wonderland in all of its 

 manifestations throughout the Grand Canyon, for that 

 will be done by Doctor Levi F. Noble for the United 

 States Geological Survey. What is intended is to bring- 

 out certain physical features of the deposits, showing the 

 shallowness of the seas of Cambrian time in the El Tovar 

 region of Arizona, the abundance of life in those seas, 

 though little of it is now preserved, and what is known 

 here of the fossils proving that their age is Middle and 

 Upper Cambrian. 



Absence of Lower Cambrian. — No Lower Cambrian 

 strata are known in the Grand Canyon area and for that 

 matter anywhere in Arizona or New Mexico. The near- 

 est known deposits of this time occur to the southwest 

 less than 200 miles in eastern California and again about 

 225 miles to the north and northwest in Utah and Nevada. 

 In the Cordilleran geosyncline the Cambrian formations 

 attain to over 12,000 feet in thickness and the Lower 

 Cambrian is generally several thousands of feet thick. 

 Against these great thicknesses within the trough, the 

 Cambrian of the Grand Canyon area averages less than 

 1000 feet in depth. In this we see that Arizona lies to the 

 east and outside of this great geosyncline and that it is on 

 the western end of the vast neutrally isostatic area of 

 North America. 



The Lower Cambrian waters were restricted in the 

 Cordillera to the geosyncline, and a wider transgression 

 did not take place until Middle Cambrian time. This 

 spreading over the low neutral area, however, was still 

 very limited, but in the Upper Cambrian the marine flood 

 transgressed widely over the United States and far to the 

 east of the Mississippi valley. The sediments of the 



