234 C. D. WALCOTT PRE-CAMBRIAN FOSSILIFEROUS FORMATIONS 



that all of these Cryptozoa are apparently more nearly related to the typical Slro- 

 matocerium ragosum of Hall from the Black River formation than to other i^troma- 

 toporoids." 



When collecting material in the Chiiar terrane in 1883 I was strongly 

 impressed with their resemblance to the forms occurring in the upper 

 Cambrian roclcs of Saratoga count}'', New York, which Professor James 

 Hall subsequently described as Cryptozoon ■p^'oUferum. There were cer- 

 tain differences of occurrence, however, that were noted at the time. 

 These were that the Chuar forms in the Grand canyon were more elevated 

 and were not semi-spherical, as most of the Saratoga forms are. Usuall}'- 

 the Chuar forms began at or near the bottom of the lawyer and gradually 

 expanded upward. If one of the specimens stopped growing or was 

 broken off, one or more began above it and continued on ujjward to the 

 top of the layers of limestone, or, as in many cases, passed the division 

 line between the two layers of limestone and continued on up toward 

 the summit of the succeeding layer. Where the specimens were very 

 abundant they were from 2 to 3 inches in diameter, whereas where the 

 specimens were scattered they have sometimes reached a diameter of 10 

 or more inches. 



The mode of occurrence strongly suggests the organic origin of the 

 forms named by Dr Dawson and j^artially illustrated on plate 23 of this 

 paper. 



Chuaria circularis, nov. g. and sp. 



(Plate 27, figures 12, 13.) 



In the sandy, slightly argillaceous shale, 730 feet beneath the summit 

 of the Chuar terrane, a number of circular, disc-like bodies were found, 

 which appear to be the remains of a compressed conical shell. I was at 

 first inclined to regard these as concretions, but, with the discovery of 

 more perfect specimens, this view was abandoned and the objects were 

 referred to as specimens of a small discinoid shell.* The specimens 

 vary in size from 2 to 5 millimeters in diameter. The}^ are concentric- 

 ally wrinkled, as though a very thin, delicate, almost membranous con- 

 ical shell had been compressed between the laminae of the shale. Usuall}' 

 a thin layer of dark bituminous matter covers the surface. When this 

 is removed the shell is smooth and shiny, veiy much like the glistening 

 surface of a phosphatic shell when slightly dulled b}^ weathering. 



The figures illustrating the form exhibit its characteristics, so far as 

 they have been determined. 



Formation and locality yielding Chuaria circularis. — Algonkian, Chuar 



*Am. Jour. Sci., vol. xxvi, 1883, p. 195. 



