WALCorr.] ARIZONA. 219 



is by Prof. T. B. Comstock. 1 He divides the rocks referred to the Cam- 

 brian into the Hickory series (Lower Cambrian?), the Eiley series 

 (Middle Cambrian?), and the Katemcy (Potsdam) series (Upper Cam- 

 brian ?). The supposition that the Lower Cambrian and Middle Cam- 

 brian are represented is based upon the presence of certain beds beneath 

 the fossiliferous Upper Cambrian. He considers that the Hickory beds 

 have altogether a thickness of 200 to 250 feet. The maximum thick- 

 ness of the Riley series is probably 300 to 400 feet. The upper or Kat- 

 emcy series is divided into, Division A, or the Potsdam sandstone, 

 thickness 90 to 140 feet; Division B, the Potsdam flags, probable thick- 

 ness 50 feet; Division C, the Potsdam limestone, 200 feet. 



ARIZONA. 



As geologist of Lieut. J. C. Ives's expedition to the Colorado Biver 

 of the West, Prof. J. S. Newberry was the first one to recognize the 

 presence of a sandstone resting upon the Archean granite in the "Big 

 Canon" of the Colorado. A diagrammatic cross-section of the cafion 

 represents the "Potsdam" sandstone unconformably superjacent to 

 the granite and conformably subjacent to strata doubtfully identified 

 as Silurian. 2 In the text it is said "the Potsdam (?) sandstone which 

 is largely developed in the Great Canon is a coarse siliceous rock that 

 must have been derived from the erosion of land at no great distance." 3 



A section at Diamond Creek, as described by the same author, in- 

 cludes a conglomerate 3 feet in thickness resting on the granite, above 

 which occurs 820 feet of sandstone. Of the upper beds of the sand- 

 stone, No. 10 of the section, Prof. Newberry says: 



The foliated sandstones of No. 10 have an indescribable look of antiquity. They 

 are usually fine grained and hard, the lighter ones drab or gray, speckled with dark 

 red. The shales above and below these sandstones are very soft red or green mud- 

 stones, containing great numbers of cylindrical bodies, which resemble the casts of 

 worm holes. 



Nos. 12 and 13 are coarse siliceous rocks, having the same appearance of extreme 

 age as No. 10, but much coarser and more massive. The lithological characters of 

 these strata are strikingly like those of much of the Potsdam saudstone of the expo- 

 sures I have examined of that rock on Lake Superior and in Canada. * # * In 

 the absence of fossils, whatever conclusions may be arrived at in regard to the age 

 of these sandstones must be in some degree conjectural and liable to modification by 

 the discovery of new facts; yet the evidence is in a good degree satisfactory that 

 they are the equivalent of the Potsdam sandstone of the New York geologists. The 

 indications of this identity are found in their great relative antiquity and in their 

 lithological characters. 4 



Attention is called to the resemblance of these sandstones to those 

 of the Black Hills which occupy the same relative stratigraphic posi- 



1 A preliminary report on the geology of the central mineral region of Texas. 1st Ann. Rep. Geol. 

 Surv. of Texas for 1889, 1890, pp. 285-289. 



2 Geological report. Report upon the Colorado River of the West, expl. in 1857-'58 by Lieut. J. C. 

 Ives. Part m, 1861, p. 42. 



8 0p.cit.,p.47. 



4 Op. cit., p. 56. 



