MESOZOIC OF SOUTHWESTERN OREGON 539 



both the gabbro and serpentine. While some prospecting work 

 has been carried on, no actual mine has yet been developed. 



Nickel. — A considerable development of nickel silicate ores has 

 taken place in the serpentine a few miles west of Riddles. This is 

 part of the serpentine belt which extends through the Roseburg 

 quadrangle continuously for over twelve miles, commencing near 

 Dodson Mountain, where the above-mentioned copper prospects 

 occur. There is strong evidence to prove that the nickel in these 

 deposits was secondarily concentrated from the olivines of the ser- 

 pentine. 1 Nickel in small quantity is a normal constituent of all the 

 serpentines associated with the Dillard. 



Chrome iron. — Chrome iron occurs in, or closely associated with, 

 the serpentines at various places, either as disseminated grains or as 

 masses, sometimes of large size. Several deposits occur west of 

 Riddles in the same hills where the nickel is found. 



Platinum. — The vicinity of the Klamath Mountains is a well- 

 known American locality for platinum and iridosmine. According 

 to Diller, these materials have been found in noteworthy propor- 

 tions in the placer mines along Sixes River, being equal to 5 per cent, 

 or more of the gold content. While the platinum has not been 

 found in its original matrix, we may, from the position of the placers, 

 conclude that it is derived from some of the formations that we have 

 under consideration, and by analogy with other occurrences it may 

 be referred to the serpentines. 



Limestone. — The Whitsett limestone lentils are of sufficient purity 

 to yield a good lime, and have been more or less used for that purpose. 

 Certain parts have yielded variegated marbles which were cut in 

 slabs and polished; but at present these are not being worked. 



Sandstones and cherts.-— Despite their superior lithification, the 

 Dillard sandstones are so crushed and irregularly veined and frac- 

 tured — especially those which have experienced the greater amount 

 of cementation — that they are only occasionally suitable for quarry- 

 ing or for the purposes of building. Cherts, such as occur here, have 

 in other parts of the coast proved excellent road metal, but the devel- 

 opment of this part of the country has not yet produced a demand 

 for good macadamized roads. 



1 See, further, Clarke, "Some Nickel Ores from Oregon," American Journal of 

 Science, 3d series, Vol. XXXV, pp. 483-88. 



