November, 1910. 



KNOWLEDGE. 



451 



certainty of result surpasses anything which has preceded it. 

 It furnishes a form for recording and organizing a mass of 

 observations, and intelligently appUed it is calculated to bring 

 order out of chaos, and be a potent factor in raising 

 bacteriology to the dignity of a science. 



Tested on forty-four strains of Pscudoinoiias caiiipcsfris 

 it gave constant results without breaking the species into 

 smaller groups. The author concludes that the qualitative 

 variations and apparently discordant reactions which have 

 commonly been attributed to bacteria are probably due 

 largely to faults either in observation or in technique, 

 Onantitative variations are constantly met, but these are 

 undoubtedly largely due to lack of knowledge concerning the 

 proper re\'ivifying process to be applied before determining the 

 culture characteristics. 



FUNGOID PAR.\SITES OF SC.\LE INSECTS.— 

 In the current number of the W'cst Indian Bulletin. Mr. 

 F. W. South gives a valuable account of work accomplished 

 on the infection of various scale insects with fungi. In the 

 Lesser Antilles four species of fungoid parasites occur on scale 

 insects, all of which may be artificially spread either by the 

 spore-spraying method, or the tying-in method. Experiments 

 showed that the fungi were most effective in the islands of 

 Dominica and Montserrat upon the scale insects attacking the 

 limes, but they are of general importance in all the islands. 

 The factors affecting the usefulness of these fungi are tempera- 

 ture, wind, and moisture ; of these the two last are the most 

 important locally. Mr. South concludes that the natural 

 means of controlling scale insects is that most suited to the 

 circumstances in the West Indies, both owing to the general 

 conditions and to the much smaller expense involved. 



GEOLOGY. 



By G. \V. Tyrrell, A,K.C.S., F.G.S. 



DEFORMATION OF MINERALS AND ROCKS 

 UNDER P R E S S U R E. — In the July issueof "Knowledge" 

 occurred a note in which the work of Profs. F. D, .Adams and 

 E. G. Coker on the eftects of differential pressure on marble 

 was described. Prof. Adams has extended the investigation 

 to other rocks and various rock-forming minerals. His results 

 are given in the latest number of the Journal of Geology. 

 The method of compression used was that invented by Prof, 

 Kick. The specimen is placed inside a stout open copper 

 tube, and the space between the two filled with paraffin wax, 

 alum, or some other material susceptible of deformation under 

 pressure. The ends of the tube are covered with brass plates, 

 and the whole then squeezed in a powerful press. The first 

 effect of the pressure is to force the copper tube into the 

 plates at each end and thus to form a very strong box, from 

 which nothing can escape except by the rupture of the tube, 

 A series of minerals in a scale of increasing hardness was 

 tested. Selenite, rock-salt, calcite, and fluorite (with hardness 

 under five in Moh's scale), showed distinct plastic deformation 

 with some development of twinning and cleavage. The 

 minerals with hardness greater than fi\'e showed no marked 

 change of shape, but in some cases evidence of internal move- 

 ment was obtained. Thus a perfect basal twinning was 

 developed in diopside. No plastic flow was obtained in hard 

 minerals such as quartz and garnet. These were broken 

 down and powdered under the pressure. A \'ery curious 

 phenomenon was observed in fluorspar, green crystals becoming 

 violet-coloured under pressure. The softer rocks experimented 

 on. such as Carrara marble, were readil_\- deformed, the shapes 

 assumed varj-ing with the character of the embedding material. 

 Dolomite was found to be more resistant, and movement 

 within the rock took place chiefly through the development 

 of cataclastic structure. The harder rocks, such as granite, 

 simply crumbled under the pressure. Much higher pressures 

 would be required in order to induce a flow-structure in such 

 hard rocks. 



SUBMARINE GEOLOGY,— In a recently-issued memoir 

 of the Geological Survey of Ireland, Profs. G. A. J. Cole and 



T. C. Crook discuss the rock-specimens dredged from the 

 floor of the .-Vtlantic off the coast of Ireland in relation to their 

 bearing on submarine geology. Specimens were obtained from 

 the Porcupine Bank, and from off the coasts of Galway,' Mayo, 

 Donegal, Kerry, and Rathlin Island. Oft' the north-west coast 

 little but submerged masses of rocks common in the west of 

 Ireland wtre obtained. The Porcupine Bank, however, was 

 found to be composed of an olivine gabbro, which is believed 

 to be allied to the Cainozoic gabbros of Carlingford and the 

 Inner Hebrides, It is therefore suggested that the Porcupine 

 Bank may represent the site of a Tertiary volcanic vent. 

 Another interesting point is that Eocene limestones occur in 

 the dredgings from the coast of Kerry, as well as abundant 

 relics of Cretaceous strata. These observations are held to 

 indicate a westward extension of the types of strata known in 

 the Paris basin, and are in accord with the results of 

 F, H, Worth, who obtained similar rocks from the English 

 Channel. 



GLACIAL PROTECTION .—An interesting paper by 

 Professor E. J. Garwood on " Features of Alpine Scenery due 

 to Glacial Protection," appears in the September number of 

 the Geographical Journal. The protective action of ice is 

 considered in relation to certain plateaux, aretes, cirques, 

 hanging valleys, and \alley steps in the Alps, It is not denied 

 that moving ice erodes an Alpine district. The problem is 

 whether it is more or less powerful than the ordinary agents of 

 erosion. The author considers that some characteristic Alpine 

 features might be explained on the assumption that ice, on the 

 whole, erodes less rapidly than other denuding agents, and 

 that, under certain conditions, it may act relatively as a 

 protection to the rocks beneath. Similar views have been 

 vigorously advocated in the past, and have been restated by 

 Dr. T. G. Bonney in his recent Presidential .Address to the 

 British Association. Professor Garwood's paper is illustrated 

 by many beautiful photographs of Alpine scenery. 



THE CANADIAN SHIELD.— In his Presidential Address 



to the Geological Section of the British Association, Professor 

 .\. P. Coleman dealt with the history of one of the corner- 

 stones of the earth — the Canadian Shield. This .great mass 

 of ancient gneiss and schist is for the most part destitute of 

 overlying formations save the products of Pleistocene glaciation. 

 There is here, therefore, as in the North of Scotland, the 

 meeting of geological extremes, between which is the most 

 tremendous discordance in geological history. The great 

 masses of gneiss are not, as some have thought, relics of the 

 original crust of the earth. They are definitely known to be 

 intrusive in a still more ancient formation, the Keewatin, in 

 which is found quartzite, arkose. slate, and phyllite, besides 

 metamorphosed representatives of these rocks and great 

 masses of igneous material. All the ordinary types of sediment 

 accumulated in the Keewatin sea apparently under much the 

 same conditions as they do now in modern seas. Thus the 

 ordinary processes of denudation were operating on broad 

 land areas ; rocks like granite or gneiss were weathering into 

 sand and mud. long before the Archaean mountains came into 

 existence. The pre- Keewatin land and sea-bottom have 

 disappeared, and have probably been fused and trans- 

 formed into the Laurentian gneiss. Such considerations 

 as these compel one to think of the inunense duration 

 of Pre-Cambrian time, and contrast its vistas with the 

 comparatively short period represented by the fossiliferous 

 formations. 



.Another interesting point is that the Lower Huronian, 

 which rests unconformably on a floor of Keewatin and 

 Laurentian, has a basal conglomerate which is almost 

 certainly an ancient till. It is the oldest known boulder clay, 

 and upon its denuded surface in many places rests the 

 youngest boulder clay. Professor Coleman remarks " It is 

 not a little impressive to see modern till resting on the 

 Huronian tillite and including fragments of it as boulders. It 

 is possible to break out from the modern glaciated surface 

 stones whose underside received their polish and striae in the 

 Lower Huronian. while their upper surface has been smoothed 

 and scratched bv Pleistocene ice-movements," 



