462 



SCIENTIFIC NEWS. 



[Nov. 2, 



which are mixed with one part of white arsenic. The 

 <jrain should be moistened with a little gum-water before 

 stirring in the poison. Strychnine or any other poison 

 of rapid action is not recommended, since if one member 

 of a flock falls down dead or is even taken ill, the 

 remainder fly away and never return. The chief objec- 

 tion to this plan is that, especially in severe weather, 

 harmless or even useful birds may be destroyed at the 

 same time. American observers are fully aware of the 

 fact that the " head and front " of the sparrow's offending 

 is that he drives away more useful birds, such as the 

 swallows. 



We are glad to see that the badger is recognised as 

 serviceable/ as he destroys mice and "gophers." 



The Entomologist to the Department has made a 

 number of investigations on destructive insects. Many 

 of his results will be of general value in the British 

 colonies. Mention is made of an epidemic which in 1867 

 almost extirpated one of the most dreaded enemies of 

 the American farmer, the " chinch-bug " (Bliosus leucop- 

 terus). It has now, however, reappeared, and is calculated 

 to have last year occasioned a loss to the extent of sixty 

 million dollars in nine of the States. 



In dealing with aphides, scale insects, a great step in 

 advance has been effected. A so-called " resin com- 

 pound" is made by dissolving three pounds of common 

 soda-crystals and four pounds of resin in three pints 

 of water over a fire. When properly dissolved, water 

 is slowly added, still boiling, to make up thirty-six pints 

 of liquid. This is then, whilst luke-warm, emulsified 

 with an equal measure of kerosene oil. Arsenic is then 

 added in the proportion of one pound to fifty-five of the 

 compound. This mixture, more or less diluted with 

 water, is driven over the trees infested, and destroys 

 even the "woolly blight" (Schizoneura lanigcrd) of the 

 apple-tree, known in this country as the " American 

 blight." It is said neither to injure the beneficial syrphus 

 larvae, nor the internal parasites of the plant-lice. 



Damage has been done both to potatoes and to human 

 beings by swarms of blistering-beetles (Lytta cinerea and 

 Epicauta vittata). These visitors injured the stems and 

 leaves of the potato-plant in the day, and flying into the 

 houses at night, blistered the faces and hands of the 

 inmates. 



Concerning the Colorado beetle, we find that its eggs 

 and larvas are eagerly devoured by a small carnivorous 

 beetle, Calcathus gregarius. 



The subject of vegetable pathology and of the fungi 

 which attack crops has received great attention. It can 

 scarcely be denied that the highly specialised plants and 

 trees which we cultivate are more liable to the attacks 

 both of animal and vegetable parasites than was the case 

 centuries back. The vine is, perhaps, more exposed to 

 such enemies than any other crop. The downy mildew, 

 black rot, anthracnose, and root-rot are described as 

 being destructive, and two more diseases — bitter-rot and 

 white-rot — have jately been identified. Very few other 

 fruit-trees entirely escape damage from analogous 

 enemies. Among the remedies which have been used 

 with success are the Bordeaux mixtures (sulphate of 

 copper and lime, dissolved separately) and " Sulphatine." 

 The latter is produced by mixing two and a half pounds 

 of anhydrous sulphate of copper with fifteen pounds of 

 ground sulphur and ten pounds of air-slaked lime. 



But were we to call attention to half the important 

 matter contained in this bulky volume we should quite 

 exceed permissible limits. 



THE FOUNDATION-STONES OF THE 

 EARTH'S CRUST. 



An Evening Discourse delivered by T. G. Bonney, 

 D.Sc, LL.D., F.R.S., F.G.S., etc., before the 

 British Association, on September iotk, 1888. 

 (Continued from p. 442.J 

 T ILLUSTRATIONS of the effects of direct crushing in 

 -*- a granitoid rock are common in the Alps. Those of a 

 shearing crush are magnificently developed near the 

 great overthrust faults in the north-west Highlands of 

 Scotland. 



In the former case, where a granitoid rock has been 

 affected only to a moderate extent, and the resulting rock 

 in a hand specimen would be called a gneiss without any 

 very definite mineral banding, we find that under the 

 microscope it exhibits a fragmental structure, the felspars 

 are often somewhat rounded in outline, are frequently 

 rather decomposed and speckled with minute flakes of 

 white mica of secondary origin, and commonly seem to 

 " tail off" into a sort of stream of microlithic mica, which 

 has doubtless resulted from the destruction of felspar 

 the residual silica making its appearance as minutely 

 crystalline quartz. The original quartz grains have been 

 broken up, and are now represented by smaller grains, 

 often in rudely lenticular aggregates, like little " inliers " 

 of quartzite. The original flakes of black mica have been 

 tattered and torn, and now appear as streaky clusters of 

 flakelets, often less than one-sixth the original length. In 

 extreme cases of crushing, the felspar has almost disap- 

 peared ; the constituents are all reduced in size, and the 

 rock at first sight would no longer be called a gneiss, but 

 a fine-grained mica-schist. It has become extremely 

 fissile, and the flat faces of the fragments exhibit a pecu- 

 liar sheen, as if it had received a varnish of microlithic 

 mica. In short, from a granitoid rock a microcrystalline 

 mica-schist has been produced, which, however, differs 

 markedly from the re \ to which that name is ordinarily 

 applied. 



Let us now turn to a rock of similar nature, in which 

 the effect of shearing is more conspicuous. I have 

 selected a specimen, in which, as in the first example 

 above, some of the felspar still remains in recognisable 

 fragments. These, however, are commonly destitute ot 

 the "tail" of mica-microliths, and bear, at first sight, 

 some resemblance to the broken porphyritic felspars 

 which occur in a rhyolite. The mica, whether primary, 

 but fragmental, or secondary, tends to get associated in 

 undulating layers; the quartz also has a more uniform 

 aspect and a more linear arrangement. In the most ex- 

 treme cases the felspar all but disappears (though I fancy 

 that it has here a better chance of surviving), the quartz 

 and the mica are more and more aggregated in definite 

 but thin bands, and the former, when viewed with cross- 

 ing nicols, exhibits streaks, which, for a considerable 

 distance, are almost uniform in tint, as if its molecules 

 under a stress definite in direction had acquired a polarity, 

 so that groups of these act upon light almost like a single 

 crystal. 



The effects of mechanical deformation, followed by 

 mineral change, are also remarkably conspicuous in the 

 case of pyroxenic rocks. Augite, it is well known, is by 

 no means a stable mineral, and under certain circum- 

 stances is readily transformed into hornblende. This 

 occurs in more than one way without mechanical action, 

 but of these I do not now speak. Only of late years, 

 however, has it been known that pressure can convert a 



