474 Transactio7is. 



This strongl}' suggested the fact that the metal came from both rocks. 

 Assays made of the rocks disthictly show traces of platinum, though no 

 grains were large enough to be visible to the naked eye. It appears from 

 this that here the mother rock of the metal has been distinctly identified, 

 and it is well to note the character of the two rocks. 



A very similar placer occurrence is reported in connection with the gold- 

 washings of Columbia. The district, which is near Bogota, is formed of 

 the detritus of two rivers flowing from a ridge which is itself an offslioot 

 from the Andes. As far as can be gathered, the country rock is a syenite 

 or syenitic gneiss, with a little granite and much metamorphic rock. 



The most notable formation of this kind is, however, the Ural region of 

 Russia. The actual deposits are found on the eastern slopes of the range, 

 and are limited to two localities — the valley of the Iss River and the vicinity 

 of the Town of Nizhni Tagilsk. Both regions are old land-areas which 

 have suffered protracted surface weathering and degradation. The drain- 

 age has reached a Imse-level, and consequently the concentration of heavy 

 minerals has been extreme. The rock-formations along the Iss are almost 

 exactly similar to those along the Tulamecn, in British Columl)ia. Near 

 the head of each stream are extensive outcrops of peridotite associated 

 with equally large areas of syenitic gneiss. Smaller exposures of diorite, 

 gabbro, and gabbro-diorite also occur. The other formations further down 

 are of no practical importance, since the river into which the Iss flows 

 derives nearly all its water from its tributary. To trace this platinum 

 to its mother rock Professor Saytzeff carried out some investigations. The 

 result of his tests shows that the peridotite is the chief source, but the 

 metal also occurs to a small extent in the gabbros. 



The Tagilsk region is exactly similar to the above, with peridotites, 

 gabbros, and diorites. 



Again, it was noted in 1870 by a Russian observer that the metal 

 occurred in Lapland, and the consensus of opinion seems to be that it was 

 in this case also derived from a peridotite. 



Borneo can also be cited in this connection. Platinum was found here 

 in gravels from a series of mountains which consisted of serpentine, diorite, 

 and gabbro. 



Just lately, too, it has been mentioned in the " Transactions of the 

 Institute of Mining Engineers," or more particularly in a paper by E. 

 Glasser on the " Mineral Wealth of New Caledonia," that platinum occurs 

 in placers on the Fly River, and these placers are, according to Glasser, 

 derived from the denudation of the great serpentine " massifs " which 

 occur in the neighbourhood. 



Besides these occurrences, there are several exceptional ones reported 

 from different countries. 



Beach-sands have been fomid on the Oregon coast to yield very high 

 percentages of the alloy as compared with gold. 



In Brittany, in France, the metal has been got with tin-bearing sands 

 along the coast ; and in the latest issue of the Geological Survey Proceedings 

 of Queensland mention is made and assays given of beach-sands along the 

 coast which contain quite an appreciable aniomit of the metal. 



Finally, an extraordinary case has been recorded of the presence of 

 metals of the platinum group in the ash of some Australian coals. Such 

 an occurrence has been recorded from no other district, and an assay shows 

 that the ash is quite the richest ore yet assayed for platinum. 



