472 
ANCIENT CHANGES OF THE SURFACE OF THE URAL. 
formation of magnetic iron was coincident with the outburst of one sort of trappsean 
rock (greenstone porphyry), which however posterior to stratified and other igneous 
rocks, was in itself succeeded by copper ore and serpentine, whilst the latter has 
been subsequently cut through by syenites and gi’anites. 
Amid the results of these various disturbances, we will now endeavour to indi- 
cate the period, at which the rocks of the Ural were impregnated with gold, and 
when the auriferous alluvia were formed. Looking at the Ural as a great meridian 
chain, we have already shown, that the palaeozoic and sedimentary deposits of 
which its central ridge and eastern parallels essentially consisted have, to a great 
extent, parted with their original characters, and have usually assumed a crystalline 
aspect. Issuing from the summit and eastern edge of this metamorphic mass, 
eruptive rocks form the culminating points of the chain, to the east of which and 
extending into the low countries of Siberia, other parallel lines of eruption, ranging- 
more or less from north to south, and also traversing palseozoic rocks, constitute 
an undulating zone, composed of hills of slight elevations, parallel to the chief ridge. 
These lower eastern ridges, all either composed of eruptive igneous rocks, or the 
original strata through which they have burst forth, are the chief seats of the mine- 
ral and metalliferous productions of the chain. For though auriferous detritus 
occurs, in one instance, on the western side of the watershed, that exceptional case 
is accompanied by the same phsenomena as are uniformly apparent in the eastern 
gold zones, viz. the contiguity of parallel ridges of eruptive rocks. 
The general feature of the great mass of auriferous materials being invariably 
found on the eastern flank of the chain, coupled with their almost total absence on 
its western slopes, has been already dwelt upon by Humboldt, who has shown , that 
in relation to the other geological phsenomena the formation of gold veins is of 
comparatively recent date, and little, if at all, anterior to the destruction of the 
mammoths. Having ourselves arrived at the same conclusion, we must explain 
the evidences which have led us to adopt this view, because in one material geolo- 
gical point they are independent of the reasons which influenced our great precur- 
sor. This point consists, in developing the geographical changes which the region 
has undergone in former geological epochs, and by deducing from their results, that 
the auriferous pheenomenon must have been posterior to all such early conditions. 
In the first part of this work we have endeavoured to establish, that the widely- 
spread cupriferous deposits of Permia, which occupy all the low country to the 
west of these mountains, have been derived from pre-existing eastern lands, upon 
