acteristics of an independent rock.

On the same grounds,
The appearance

greisen, too, might be logically ignored. of Limurite in Tasmania, as well as in the Pyrenees, favours the inference that it will recur wherever the necessary conditions prevail. Where emanations from cooling granite act upon calcareous strata, there axinite rock may be expected. There seems no reason why it should not bear the name first given to it by Frossard, after Count Limur.

In concluding this review of the eruptive rocks of Tas mania, I may mention that I have omitted allusion to many occurrences which are known from hand-specimens, but which have not been examined in the field.

From a scientific point of view the rocks which are the most interesting are those which possess unusual associations, such as the melilite basalt at Sandy Bay, the diorite at Port Cygnet in a plexus of elæolitic rocks, the trachydolerite at Table Cape associated with normal olivine basalt, the hypersthene basalt at Stanley. All of these require careful working out on the spot. The nephelinite and melilite basalt at Shannon Tier are also in a part of the Island where normal olivine basalt occurs. The recent discoveries show that the basalts of the Island are far more varied than has been anticipated, and the relations of their magmas to each other demand rigid study.

AN INTERESTING OCCURRENCE OF GOLD IN

VICTORIA.

By HENRY C. JENKINS, A.R.S.M., Assoc. M.Inst., C.E.

AT Clombinane, about six miles from Wandong, on the Melbourne to Sydney Railway, there are two mines the "Golden Dyke" and the "Golden Dyke Extended ”—that present some features of interest, as bearing upon the general problems connected with the occurrence of gold in Victoria.

The mines are both in a true dyke, cutting roughly east and west across Upper Silurian country. Its width is from 50 up to 200 feet, and it belongs to the so-called intermediate class of rocks. The present workings of the two mines cover about a quarter of a mile in length; along the dyke, and midway between them, there is a gully that has been very rich in alluvial gold, just where it crosses the line of dyke, the gold being evidently derived from the denuded dyke-mass, which latter so readily decomposes and softens that, at the time of my first inspection, I could not obtain any satisfactory specimens for slicing; it is, indeed, only very recently that some have come to hand from the deeper workings too late for full examination and analysis.*

The general mass of the dyke is quite worthless as a gold ore, notwithstanding that it carries arsenical pyrites in its partings, but transversely across the dyke, and nearly at right angles from wall to wall, numerous groups of small cross-seams occur; these extend vertically or else are replaced by others, so that each level in the mine presents somewhat similar features to those of its neighbour. The veins are found by driving levels along the line of the dyke, and they are stoped from crosscuts along them as they are found. The workings are now about 360 feet deep from the surface at their deepest part.

The veins are filled in with quartz, limonite, stibnite, and derived oxide of antimony, and are rich in gold. They can be followed across the dyke up to the wall of the same, where they disappear rapidly, and within a foot or so of the contact-plane, just as though they only occupied fissures in the dyke-mass caused by a shrinkage of the same, such as would be produced by cooling. Some of the quartz is beautifully crystallised, and gold is found upon and in it;

The rock proves on examination to be an andesite almost entirely composed of minute felspars, with phenocrysts, also of felspar.

but the bulk of the gold is found in a finely crystallised form upon rather than in the stibnite, exactly as though it has been precipitated with quartz at a much later period than that at which the filling of the veins with antimony had taken place, and probably by the direct action of the latter. At times much of the gold can be separated in quite coarse grains from the rest of the vein-fillings by simple crushing or rubbing.

The evidence of precipitation upon an earlier deposit of antimony is a feature that is well worth special notice, and sometimes this is particularly well marked; one specimen in my possession is a small sheet of antimony about a quarter of an inch thick, once part of a much larger sheet, thickly coated over with finely crystalline gold. This was from a crevice that had somewhat exposed the mineral. In the denser parts of the deposit the gold seems to occur more in crevices in the antimony.

The deposit is interesting, as showing clearly that the auriferous contents were acquired at the last stage of formation, and has been precipitated on stibnite that had been deposited at a prior date.

IN

ROCK TEMPERATURES AND THE RATE OF INCREASE WITH INCREASED DEPTHS VICTORIA.

By HENRY C. JENKINS, A.R.S.M., Assoc. M.Inst. C.E.,

Government Metallurgist, Victoria.

THE importance of some knowledge as to the rate of the increase of temperature as we descend in the earth appeals both to the geologist and to the miner; to the former as being the starting-point of many interesting and important speculations, and to the latter because it points out at once a superior limit of depth beyond which he cannot hope to carry on his work without availing himself of some means by which he can cool his workings. The taking of steps to secure this end must add to the cost of his operations, and finally put a stop altogether to them by making them unprofitable; indeed, the rise of temperature must put a limit to the depth at which mining operations can be carried on, either upon purely physical grounds or upon purely economic

ones.