749 
contact with rocks of igneous origin, in which serpentine, compact 
felspar, greenstone, porphyry, &c. are apparent. At Nijny Tagilsk 
the chief intrusive rock (greenstone) is coated by prodigious masses 
of the iron ore, which is worked in open quarries, and is most mag- 
netic where it is in contact with greenstone. Copper ores also 
abound at this spot, and some of them are associated with Silurian 
limestone, often highly mineralized, but in which large Pentameri 
and other fossils are observed ; also with a bedded trappean rock or 
schaalstein, which is in parts highly cupriferous. It is from such 
ancient rocks that copper solutions are supposed to have flowed, in 
very remote periods, into the adjacent low countries on the west, 
then under the sea, and to have impregnated the sandstones and 
grits of Perm during their formation. The malachites of this place 
have long been celebrated, and, from their structure as well as their 
position, in cavities of the rock, they are supposed to have been 
formed by ancient stalactitic depositions. ‘The ores of platinum, 
though hitherto found in alluvia only, always occur near the pro- 
trusive igneous rocks. Magnetic iron oreand copper ore are stated 
to occur at many other localities, and always under similar circum- 
stances. 
Gold Ores.—Though the great supply of gold which the Urai 
mountains afford, is derived from alluvia, the ore has been found in 
veins which are slightly worked at Berosofsk, near Ekaterinburg, 
and were formerly near Miask*. Wherever gold veins or gold 
alluvia have been discovered, the auriferous matter is flanked by 
rocks of intrusive origin, and these are very frequently serpentine. 
It has however been shown by Humboldt and Rose, who, in the first 
volume of their recent work, have described twenty-seven sites 
of gold alluvia in these mountains, that the auriferous detritus 
rests upon a great variety of rocks, viz. talcose, chloritic, siliceous, 
argillaceous schists and encrinite limestone, as well as upon 
granite, greenstone and serpentine, though most frequently on the 
last-mentioned rock. An observation also of these authors is im- 
portant, as bearing upon the relative date of the origin of gold, 
viz. that the veins containing it have been seen by them to cut 
through not only the schists and the beresite (according to them 
a felspathic granite), but also the serpentine ; thus seeming to prove 
that the gold veins have resulted from one of the very last changes 
which have affected this region. (Rose, vol. i. p. 422.) 
It is stated, that as the alluvia containing gold are purely of local 
origin, or derived from the adjacent hills, their accumulation can 
have no reference to the actual period, and present rivulets or 
waters, for the deposits Jie at considerable heights above their beds, 
contain bones of mammoths, the extinct rhinoceros, and, in some 
* In the tracts around Miask and Zlataoust the authors were most 
cordially and judiciously assisted by General Anosof, an officer highly 
distinguished for the metallurgic processes and the manufacture of small- 
arms which he directs. His assistant, Major Lissenko, who has prepared 
a mineralogical map of the surrounding country, was also kindly serviceable 
to them. 
3p 2 
