Page:Quarterly Journal of the Geological Society of London, vol. 28.djvu/362

304 Of this Mr. Allport says:—

"It contains a fibrous green mineral, which appears to be hornblende, partially altered; the felspar is very opaque and indistinct in form.

"The base contains much chlorite and a few blebs of quartz, together with a little epidote.

"The rock is highly altered; and if the green fibrous mineral should turn out to be uralite, it might then be called a diabase."

All the rooks of this group, indeed, are much altered, generally in the direction of serpentine; their specific gravity varies from 2·700 to 3•100, according to the proportion of pyrites, hornblende, or chlorite entering into their composition. The general facies corresponds with that of the intrusive dykes of the Wood's Point District, in Victoria, where similar geological conditions produce similar mineral results.

The serpentines containing chromic iron, rarely pyrites, are in my opinion simply altered forms of Group 2.

In the Gladstone, Cawarral, and Kilkivan districts, there is constant evidence of this; and in the first-mentioned district it is especially marked.

This group is very sparingly represented in Queensland, the most noticeable instance being that of Mount Wheeler, the analysis of which by the late Professor Thompson, of the University of Sydney, is as follows:—

Mount Wheeler "Felsite."

Undecomposed by HCl 9675

Decomposed 3·25

Undecomposed. Decomposed.

Silica 76·28 Silica 36·54

Alumina 12·64 Alumina 23·97

Ferric oxide 0·92 Ferric oxide 11·59

Ferrous oxide 0·85 Ferrous oxide none.

Lime 0·33 Lime 1·57

Magnesia trace Magnesia trace.

Potash 3·30 Potash 1·14

Soda 4·59 Soda 2·00

Water 0·16 Water 19·98

99·07 96·79

Specific gravity 2·564.

This rock rises abruptly to an elevation of 800 feet, through serpentine, gabbro, and diallage rock. It is very close-grained and