226 



NATURE 



[July 6, 1893 



Tavel writes more fairly with regard to the work done by 

 other schools, and has wisely avoided the bitter methods 

 adopted by Brefeld towards De Bary's pupils in some of 

 his volumes, there still seems to persist a tone of 

 under-valuation of the work of the Strasburg school. 

 After all, it should never be forgotten that unless De 

 Bary and his pupils had followed up the clue — how- 

 ever false it may prove — of the "sexuality" of 

 the ascomycetes, the matter would have had to be 

 investigated, and the fact that the Munster school is 

 enabled to explain the phenomena seen in a new sense 

 proves how valuable De Bary's careful observations were. 

 Moreover, however probable Brefeld's view of the origin 

 of the ascomycetous series is — and it is now the clearest 

 story yet put forward — many of his own facts show that 

 the impossibility of De Bary's view of a sexual origin, 

 now lost, of the ascocarp, is by no means proved. Brefeld 

 insists that the simplest ascocarp (e.g. Thelebolus) may be 

 derived by suppressing the stalk and withdrawing the 

 sporangium of a form like Afortierella into the investing 

 barren hyphse at its base ; but the zygote of Mortierella 

 also has investing hypha;, and it would not be going 

 much further to suppose the sporangium of the ger- 

 minated zygospore of such a form to be similarly with- 

 4rawn into the invested capsule. This " wild hypothesis " 

 would not alter Brefeld's view as to the homology of the 

 ascus, or the derivation of the ascomycetes from the 

 zygomycetes, but it would, and very materially, alter the 

 attitude adopted towards the sexual hypothesis. We 

 have termed the suggestion " wild," but it is pos- 

 sibly not more so than Brefeld's own hypothesis as 

 to the nature and evolution of the chlamydospore, 

 and we imagine that the last word has not yet 

 been said on either matter. However that may be, 

 Brefeld's laurels of results are such as are won by very 

 ■few investigators and Von Tavel is to be congratulated 

 not only for his own discoveries, but also on his book, 

 which is by far the best exposition of the subject in 

 ■existence. 



H. M.\RSHALL Ward. 



DAUBRltE ON THE GEOLOGICAL WORK OF 

 HIGH PRESSURE GAS. 



A SERIES of experimental researches which promise 

 -'"^ to lead to important results, and which have 

 already been applied by their author to the explanation 

 of some difficult geological problems, have during the 

 last few years been carried on by M. Daubrde. These 

 experiments are concerned with the action of rapidly 

 moving and high-pressure gas on rock masses, and lead 

 ■to the conclusion that such high-pressure gas is a geo- 

 logical agent of no small importance. To carry out 

 such experiments is no easy matter, but M. Daubr^e has 

 been fortunate enough to obtain the use of the apparatus 

 used in the testing of explosives in the Laboratoire 

 Centrale des Poudres et Saltpetres. The high-pressure 

 gas has been obtained by the explosion of gun-cotton 

 and dynamite, the explosions being made in a steel 

 cylinder with very thick walls, and closed at both ends 

 with steel plugs. One of these plugs is fitted with a 

 platinum wire, by the heating of which the charge can 

 be exploded. The other, which under ordinary circum- 

 stances contains the manometer for measuring the force 

 of an explosion, is modified so as to contain a block of 

 the rock to be experimented on. A circular hole, more- 

 over, is made at one end so that the gas, after traversing 

 the rock, is allowed to escape. The rock, cut in the form 

 of a cylinder, is supported between a steel stopper and 

 the head of a piston. The charge of gun-cotton or 

 dynamite usually filled a tenth part of the interior, and 

 Jthe pressures obtained were from iioo to 1700 atmo- 



NO. 1236, VOL. 48] 



spheres. In one experiment the pressure was increased 

 to,' 2300, and in another the still greater pressure of 

 2400 atmospheres was obtained. Many different kinds 

 of rock were used, such as limestone, gypsum, slate, and 

 granite, and each cylindrical block experimented on was 

 cut through by a diametrical plane. In some of the 

 experiments an additional very fine perforation was made 

 along this plane. 



As a result of the sudden shock of the explosions 

 most of the rocks were fractured. In the case of the 

 slate this resulted in faulting. The limjstone and 

 granite were broken up and crushed, but under the influ- 

 ence of the pressure the small fragments were quickly 

 consolidated so as to resemble the original rock. This 

 property of reconsolidating under pressure, thus shown 

 to be possessed by rocks, seems analogous to the plas- 

 ticity of ice observed by Tyndall. 



All the rocks experimented upon, even the most 

 tenacious, have undergone more or less erosion. The 

 gases have disintegrated and pulverised them, and 

 carried out \\\z fragments. When their action was con- 

 centrated along certain lines, true perforations — that is to 

 say, rounded channels more or less regular — were eroded 

 through the blocks. In the case of a granite block the 

 original perforation of i '2 mm. was increased to a channel 

 of 1 1 mm. The walls of these perforations after the 

 explosions were found to be striated and polished. 

 Sometimes the striations are parallel, like those pro- 

 duced by ice. At other times they spread in fan-form, 

 and sometimes they are sliyhtly curved. 



The products of erosion are thrown out into the 

 atmosphere, and an examination of the powder thus pr> 

 duced shows that a portion of the same possesses an 

 interesting resemblance to the dust usually held to be of 

 cosmic origin. 



M. Daubr^e applies the results of his experiments to 

 explain the remarkable " diamond pipes " of South 

 Africa. These diamond deposits are described tiy M. 

 Mouelle in the Annates des Mines (tome vii. p. 193, 

 1885) as filling in cylindrical cavities of unknown deptlu 

 in the rocks. These cavities appear to be cut out of the 

 subjacent sedimentary or eruptive rocks, their upper 

 parts are filled with a soft yellow decomposed rock 

 matter, while below they contain liard volcanic con- 

 glomerate. They vary in size from a diameter of 20 to 

 one of 450 m., and are originally surmounted by slight 

 eminences, known as kopyes (little heads). 



An interesting point about the general arrangement of 

 the " pipes" is their occurrence along a straight line of 

 200 kilometres in length. Their walls, again, are smoothed 

 and finely striated. These striations are often parallel, 

 and indicate a powerful thrust from below upwards. No 

 alteration is observable in the beds of shale forming the 

 walls, except a slight elevation of their edges. 



Thus in their general form, as long, narrow, cylindrical 

 perforations in the earth's crust, they resemble the arti- 

 ficially produced perforations in the rocks experimented 

 on. Their arrangement along a straight line suggests 

 that they may have been opened along a line of fracture 

 as were the perforations in the experiments. In the 

 latter, the line of the eroded channel was determined by 

 a very narrow perforation, and M. Daubrce suggests 

 that in the former the positions of the "pipes" may 

 have been determined in some cases by cross-fractures. 

 The polishing and striation of the walls of the diamond 

 pipes, again, is reproduced in the polishing and striation 

 of the perforations in the experiments. 



Another application of his experimental results made 

 by .M. Daubree is to explain the opening out of the 

 channels by which volcanic products reach the surface. 

 Here, again, the linear arrangement of volcanoes, which 

 has been so fretjuently pointed out, is noted as connect- 

 ing volcanic vents with the experimental results. These 

 are supposed to lie along lines of fracture, and each 



