476 G. King— Geology of the. ^Olh Parallel 



key to the subdivision of the whole Paleozoic is obtained in 

 the Wahsatch Eange, where I have observed a single section of 

 about 30,000 feet of conformable rocks extending from the 

 Permo-carboniferous strata, conformably underlying the red 

 sandstones of the Trias, down to low exposures of the Cambrian. 



'sion -.-... 



able and local, and describing only 

 I, I wiir 1 



Ignoring such minor subdivisions as we find to be very vari- 

 ble and local, and describing only such as are observed to be 

 lersistent and widespread, I will note in their order from the 



3 of the Cambrian upward the important stratigraphical s 

 divisions, with their position in the Kew York scheme. 



The lowest member of the series consists of a group which 

 rests non-conformably upon the Archaean, and consists of three 

 prominent members : the lowest is a series of siliceous schists 

 and argillites, best exposed at the mouth of Big Cottonwood 

 Canon, in the Wahsatch Eange, and having a total thickness of 

 from 800 to 1,000 feet ; over this is a series of quartzite and 

 quartzofeldsitic strata, having limited beds of slate interspersed 

 through it and containing near the top some dark micaceous 

 zones, the whole reaching in Cottonwood Canon a thickness of 

 over 12,000 feet : the uppermost member is a narrow zone of 

 variable argillites, calcareous shales, and thin, slightly siliceous 

 limestones having in the Wahsatch an extreme thickness of 

 seventy-five feet. The sbaley zone and the accompanying slates 

 carry fossils of well-defined Primordial types, but the quartzite 

 and the deep-lying slates have not yet yielded any organic 

 forms. We have therefore in the Wahsatch a series of 12,000 

 feet, of which the thin summit member carries Primordial fos- 

 sils, and the vast underlying series is thus far barren. Com- 

 paring the quartzites and argillites with those of the Cambrian 

 section in Wales, the likeness is too great to pass unnoticed, and 

 in view of the enormous developments of these low-lying 

 rocks, as compared with the Silurian lying above the Primor- 

 dial horizon, I have determined to draw a line at the upper 

 limits of the Primordial period to include the uppermost mem- 

 bers of the Potsdam epoch, and to consider the whole under- 

 lying conformable series as Cambrian down to the point of their 

 non-conformity with the Archaean. In the extreme east of our 

 work, in the region of the Rocky Mountains, the Cambrian 

 formation is of variable thickness and nowhere reaches an ex- 

 posure of over 100 feet. In middle Nevada the uppermost zone 

 of the Cambrian, equivalent to the calcareous and argillaceous 

 shales of the Wahsatch, is an immense bodv of dark limestones 

 at least 3,000 feet in thickness carrying Primordial fossils 

 throughout; the downward continuation of the series being 

 there entirely hidden by the overlying Quaternary desert. 1 he 

 fossils obtained by our survey from the Cambrian series are as 

 follows : 



