300 
GEOLOGY* 
in the direction of two opposite basal edges, and was tbns an imperfect rectangular octahedron. 
Its greatest length of base is one inch, and in the other direction it is seven-eighths of an inch. 
When found, all the spaces between the interior plates of gold were charged with a hard crust 
of peroxide of iron. 
The most beautiful specimens of crystalline gold are those in which the crystals are combined 
with an arborescent or dendritic growth of the metal like the leaves of ferns or the foliage of the 
arbor vitee. Specimens of this character are not found among the rudely transported drift, but 
can be obtained only from their original bed in the solid rocks. Some of the most remarkable 
and beautiful specimens ever seen were taken out of the cavities of a quartz vein at Irish Creek, 
about three miles from Coloma. They presented various and complicated combinations, being 
arborescent, in broad, paper-like sheets, studded with brilliant crystals, and in solid octahedrons. 
These were combined together in the most interesting manner, giving an effect far beyond the 
reach of art. 
A very fine specimen of this character in my collection has the form of a leaf; one side is 
arborescent and very brilliant, and the other is studded with about twenty-five perfect octahedral 
crystals. They are geometrically arranged, all their similar edges being parallel. This is 
believed to be the most beautiful and curious specimen known. Its weight is seventeen penny¬ 
weights and ten grains. Length, two and one-quarter inches ; width, one and a half. 
One of the largest specimens of this arborescent and foliated gold from Irish Creek was about 
twelve inches long and about four broad. A part of the specimen was a plate three or four 
inches long, covered with triangular marks ; the remainder was arborescent, and the whole 
appeared to have grown from one end. Another specimen, slightly different in its character, and 
probably from another locality in the vicinity, was ten inches long, three broad, and about half 
an inch thick. It weighed thirty-one ounces, and was free from quartz; forming a most beautiful 
mass of a rich yellow color, and a delicately-marked surface, consisting of a net-work of fibres. 
It appeared like a bundle of broken fern-leaves closely matted together. 
With one exception, all of the crystals which have come under my observation are octahedrons; 
not a single cube has been seen. The exception is a single crystal, a pentagonal dodecahedron, 
upon one of the broad plates of gold. 
PLATINUM AND IKIDOSMINE—PLATINIKIDIUM. 
Grains and scales of Platinum, Iridosmine, and the associate metals, occur with the gold in 
almost all parts of the great gold-field, but are most abundant in the northern mines. These 
metals constitute a very large part of the product of the washing of the black sands of the beach 
at Port Orford and the coast in its vicinity. They cannot be separated from the thin scales of 
gold by washing, and amalgamation with mercury is resorted to by the miners to obtain the 
latter. After the removal of the gold the residue is found to consist, in part, of round, flattened ! 
scales of Platinum or Platiniridium, which are mostly lifted by a magnet. Two or three ounces 
of this residue were obtained in San Francisco from a miner who had returned from the locality, 
and a portion of the sample was submitted to Dr. F. A. Genth, of Philadelphia, for chemical 
investigation. An analysis was made in his laboratory by Mr. Charles A. Kurlbaum, jr., with 
the following results : 
Insoluble in aqua regia, (Osmiridium). 48.77 
Platinum. 43 - 54 
Iridium. °- 60 
Rhodium............ 
