356 THE CAMBRTAN. Ibull.81. 



Kateincy (Potsdam) series (Upper Cambrian ?). This upper series is 

 divided into Division A, the Potsdam sandstone ; Division B, the Pots- 

 dam flags ; Division O, the Potsdam limestone. 



ARIZONA. 



t 



As far as known the Cambrian rocks of Arizona are confined to the 

 sections exposed by the Grand Canon of the Colorado and along the 

 southwestern margin of the great Colorado Caiion plateau. 



A section measured near the head of the Grand Canon has 300 feet 

 of sandstone at the base that rests unconformably upon the subjacent 

 Algonkian (Chuar) formation. Above the sandstone there are 700 feet 

 of alternating sandstones, shales, and limestones throughout which fos- 

 sils of the Upper Cambrian zone have been found. These include the 

 genera Cruziaua, Lingulepis, Iphidea, and Ptychoparia. At the summit 

 of the lower sandstone a small group of fossils was found which includes 

 the genera Olenoides, Ptychoparia, Lingulepis, and Leperditia. The 

 upper part shows close relation to that of the Potsdam sandstone hori- 

 zon of central Nevada, the Mississippi Valley, and New York, while 

 that of the lower zone or the summit of the sandstone is more nearly 

 related to that of the Middle Cambrian zone of the Southern Appa- 

 lachians. There is a large quantity of material in the laboratory of the 

 U. S. Geological Survey yet remaining to be studied, but I think these 

 conclusions will not be materially changed. 



At the month of Kanab Creek, west of the Kaibab Plateau, there are 

 100 feet of arenaceous and micaceous shales, subjacent to a massive 

 stratum of mottled limestone. In the lower 450 feet of the latter and 

 in the arenaceous shale fossils were found similar in character to those 

 of the upper portion of the section, as seen near the head of the canon. 

 They include Lingulepis, Hyolithes, and Ptychoparia. 



The section at the mouth of the Grand Canon, as given by Mr. A. 

 E. Marvin e, is as follows : ] 



Feet. 

 Red wall limestones. 



Tonto marble limestones. 



Tonto sbales 



(Green j ^ 



' \ Snuff-colored 90 



(Green 415 



Tonto sandstone 80 



Granite 90 



Mr. Marvine says that in going southward from the mouth of the 

 canon the Tonto shales seem to diminish in thickness, and at Tinnakah 

 Springs they are estimated at less than 400 feet. A few miles south 

 of this point they were still thinner, being estimated at less than 100 

 feet. . The Tonto sandstone, however, has increased much in thickness 

 and forms the greater portion of the section. 



' Report on the geology of route from St. George, Utah, to Gila Hirer. Arizona, examined in 1871 

 Rep. on Geog. and Geol. Expl. and Sui v. west of 100th rnerid., in charge of Lieut. Geo. M. Wheeler, 

 vol. 3, Geology, 1875, p. 199. 



