xlvi 



quantity alieady in our forests, the 

 enhanced value owing to increased care in 

 growins: would not repay the cost of atten- 

 tion. This, however, does not apply to the 

 growth of w-attle bark. Probably system- 

 atic planting of black wattle would pay 

 handsomely^iu any district, and in many 

 poor grazing districts would return a sum 

 at the end of a few years that L.he owners 

 of the land have little idea of. The class 

 of trees required are such that would 

 yield the best class of deal within a reason- 

 able time. Such trees are found only 

 amongst the fir or pine family. Last year 

 about £18,000 worth of such wood was 

 imported. The systematic growth of 

 forests is largely practised in older coun- 

 tries of the world. In Germany recently 

 35,000,000 acres are so employed, returning 

 £21,000,000 sterling, and employing over 

 half a million persons. Tasmania is 

 peculiarly suited for the growth of the best 

 class of' timber, and it is deplorable 

 that the industry has not received 

 the attention of our governing bodies. 

 But the most important reason for en- 

 couraging tree-planting is not from the 

 return of timber, but for the conservation 

 of the water that is allowed to flow so 

 ruthlessly to waste. A well timbered 

 country retains the M-ater from rains as a 

 sponge would, allowing it to drain out very 

 slowly, so that if we had reasonable forest 

 areas on our watersheds, instead of a rush 

 of rainwater to get off the land alternating 

 flooded with dry creeks, the outpouring 

 would be so slovv that most of our creeks 

 would more assume the character of a 

 brook with a constant mean level. The 

 rainfall of Tasmania is not so small as 

 generallv supposed, only the ubiquitous 

 gum and extensive clearings constitute 

 poor reservoirs. A forest, to be effective 

 both for growth and water conservation, 

 must maintain an unbroken and almost 

 impenetrable canopy of foliage. Though 

 climate is mostly due to cosmic 

 causes, still local influences often go 

 largely towards determining precipitation. 

 Forests tend to equalise temperature, 

 and masses of atmosphere heavily charged 

 with moisture will, over a clear, dry, hot 

 area become rarified, whereas over a 

 cooler, damp district, i-ain must fall. But 

 it is not only in the vexed question of 

 rainfall that forests influence climate, it is 

 also in their immediately local influences 

 that they are of value. The rigours both of 

 summer and winter would be greatly 

 mollified, and many bleak portions of 

 Tasmania rendered reproductive were 

 judicious planting encouraged. If due 

 encouragement had been given to this 

 subject, say, even in the days of the 

 sixties, we should now be not only pro- 

 ducing all the softwood we require, but 

 should be supplying the still larger market 

 of Australia, and be in a position to do so 



for all time. Should we not in our own 

 interest, as well as the interest of those to 

 come after us, give this our earnest atten- 

 tion at once? 



Messrs. W. H. Twelvetrees, F.G.S. 

 (Government Geologist), and W. F. Pet- 

 terd, C.M.Z.S., submitted an interesting 

 paper, entitled, " On the Mesozoic 

 Dolerite and Diabase in Tasmania." The 

 writers stated that the subject of the 

 paper is the familiar diabase or dolerite 

 rock which plays such an important part 

 in the geology and physical configuration 

 of Tasmania. The geographical distribu- 

 tion of this eruptive rock in the island is 

 briefly stated, and the striking fact referred 

 to, that it is nearly invariably associated 

 with permo-carboniferous and trias-jura 

 sedimentary strata. The theory that the 

 igneous rock is a sill concealing the sedi- 

 mentary beds below it is mentioned, but 

 conclusive evidence is said to be stiil 

 wanting as to whether it is a denuded 

 intrusive sheet, or a vast eruptive mass in 

 situ. The thickest known sills are stated 

 to fall short of the development of the 

 massive rock which forms the upper part 

 of Mount Wellington. The geological 

 horizon of the rocR is considered to be at 

 the close of the trias-jura, or beginning of 

 the tertiary, and the microscopical appear- 

 ance of samples from all parts of the 

 island support the inference that the rock 

 all over the colony belong to one and the 

 same geological age. It has never been 

 found in situ in tertiary beds. In one in- 

 stance microscopical fragments have been 

 noticed included in tertiary olivine-basalt. 

 This occurs near Bothwell, where the 

 basalt has probably entangled in its flow 

 loose pieces of the older rock. The essential 

 minerals are plagioclase-felspar and augite. 

 The accessory ones are olivine, apatite, 

 elmenite, magnetite, pyrite, mica, and 

 quartz. The secondary minerals which 

 have been developed are chlorite, serpen- 

 tine, actinalite, calcite, and scolecite. After 

 a description of the microscopical char- 

 acters of the rock, the authors state that 

 locally the dolerite becomes converted 

 into diabase by the chloritisation of the 

 augite. The nearest European types 

 with which the Tasmanian rock may 

 be compared are the hunne-diabase and 

 kinne-diabase in Sweden. It has been 

 produced by the crystallisation of a magma, 

 which was injected or intruded into 

 strata lying below the surface. It did not 

 crystallise rapidly, but under the pressure 

 of superincumbent rocks now removed by 

 denudation. There is nothing to show 

 that the molten rock ever succeeded in 

 establishing communication with the sur- 

 face. If, however, it did, both the pipes 

 by which it ascended, and the basaltic 

 flows in which the ascent finally resulted, 

 have been wasted, without leaving a trace 



