374 CD. Walcott — Position of the Olenellus Fauna. 



for platinum, by the following method : One assay ton of the 

 finely ground ore was treated with nitric acid until all or prac- 

 tically all of the sulphides had been dissolved. The dried 

 residue was then assayed in the usual manner ; except that, to 

 facilitate cupellation, a little pure silver was introduced iuto 

 the lead button. From the final bead the silver was dissolved 

 out by sulphuric acid, leavin'g the platinum in a finely divided 

 gray powder. The latter dissolved easily in aqua regia, and 

 gave all the reactions needful to identify it thoroughly. The 

 results were as follows, "A" representing the large mass in 

 which the polydymite was determined. 



A, 2-55 oz. Pt to the ton, or 0-0087 per cent. 



B, 1-8 " " -0060 " 



C, 7- " " '024 " 



That the metal weighed was nearly all platinum is certain ; 

 but it may have contained small amounts of other metals of 

 the same group. The material separated was not sufficient to 

 warrant a search for the rarer associates of platinum. Probably 

 the platinum exists in the ore as sperrylite, although this point 

 was not proved. The amount of platinum in the mass most 

 thoroughly examined would require, to form sperrylite only 

 about 0'007 per cent of arsenic, which is too small a quantity 

 for detection by ordinary analysis. That platinum should exist 

 in appreciable quantities in an ore of such character is some- 

 thing quite extraordinary. Whether it could be profitably ex- 

 tracted is an open question. 

 Washington, Feb. 2, 1 889. 



Art. XL. — Stratigraphic Position of the Olenellus Fauna 

 in North America and Furope ; by Chas. D. Walcott, 

 of the TJ. S. Geological Survey.* 



In reviewing the history of American opinion on the succes- 

 sion of the Cambrian faunas, we find that the first systematic 

 arrangement of the terranes containing them was made by Sir 

 William Logan, on the basis of the paleontological determina- 

 tions of Mr. E. Billings. In a table published on page 46 of 

 the report of the Geological Survey of Newfoundland for 

 1864, the order of succession of the Lower members of the 

 series is : 



3. Upper Potsdam. 



2. Lower Potsdam. 



1. St. John's Group. 



* Read before the Philosophical Society of Washington, March 16, 1889. 



