Maitlaxd. — ircsicni Australian Geology, 
215 
I'licso rocks foj'iii ]>ai't of that liow-shapod j>rcal circle ‘wliicli 
ia I'^re-Camln-iaii times extended from Western Australia across the 
i!.ortli-easteru portion (-f the Indian Ocean, tliron^di Peninsular India, 
tile Hindoo Koosh .Mountains, down wliat is now tiie valley of the 
Oxus, and thence along' that narrow i)elt between Kastei'ii Hiirox>e 
and Mh-steni Asia — the Pra! .Mountains- and disapx)earing bemmth 
the waters of tlie Arctic Ocean in the vicinity of Nova Zeinbla and 
the Kara Sea. 
Tile I'leds in Peninsula India ha\U‘ the same general treml, 
lithological character, tectonic structure and community of origin 
as Their Western Australian re^iresentat iv's. They disappear l)(‘- 
neath that enormous develo])ment of horizontal basaltic lava flows, 
the Deccan Tiaips of (Vntral India, veaiipearing in Udaixmr ami 
emerging from beneath the recent IkmIs of the Indo-Gangetic Pl.ain 
in tlie froiiTii'r rangi-s wliitdi sejiarate the Indian Kmjiire from 
Afghanistan and Turkestan. In the Hindoo Koosh Mountains frag- 
ments of these Pre-Cambrian rocks still exist, though much broken 
and shattered by those biter earth movements which raised the 
Alpine-Ilimahiyaii and Dutcli Past Indies mountains during the 
Tertiary period, and which crossed the former almost at right 
angles, thus dividing the liemisjihere into two halves. 
Crossiiig the Himalayas and the fi-ontier ranges, the beds 
n‘a]i]M‘nj' in tlie Ural Mountains. Here is a long belt of crystal- 
line and metamorpliic sedimentary rocks associated as in India and 
Western Australia witli tliose characteristic red and other coloured 
ribbon jasjiers, in addition to being invaded by gold-bearing acid 
dykes and ([iiartz reefs. 
Over the vast area of this Great Circle, there is a surprising 
uniformity in the cliaracter of the mineral dexmsits, as regards 
alike tludr geological ndations ami tlieir structural and mineralogicnl 
features. 
These long lim's of weakness and moliility are also the zones 
of greatest vulcaiiism and concomitant ('artlnpiake activity. Vol- 
canic. eruxitions, together with tludr cognate activities are tlie con- 
sequences of tlii^ major moviunents affiuding the earth ’s crust, and 
Xn-oduce, inter alia, a general himting and local iiicrenumts of the 
temperature gradimit. it is for tliis reason that the central ])0i- 
tion of Wh'.stern Australia in the regions of the geo synelino to 
which previous refereiici* lias lieen made, has revelled in a long 
poriod of igneous activity, Nvith its great crushing and folding 
movemoiits, in the Pre-Candndan xandod of its geological history. 
The volcanic and allied igneous I’ocks, several of which arc 
lavas, some sills, and others differentiation products, are in many 
areas much more abundant than the sedimentary members, though 
