July 6, 1893] 



NATURE 



227 



volcano is supposed to have been determined by a cross 

 fracture, or some other cause, facilitating the passage of 

 gas at that particular point. That there are reservoirs 

 of gaseous pressure of great power below the surface is 

 evident from volcanic phenomena generally, and given a 

 line of fracture, with cross fractures, or other predispos- 

 ing causes, the experiments prove that high pressure gas 

 is capable of opening out cylindrical passages by which 

 molten rock matter and fragments may reach the surface; 

 In this connection, M. Daubree points out the occurrence 

 of volcanic craters, of which the cones are formed 

 entirely of rock fragments, and known as " craters of 

 explosion." Thus, near Confolens, in Velay, there is a 

 crater excavated in the granite, and of which the cone is 

 formed entirely of granitic fragments. 



M. Daubree further applies his experiments to explain, 

 ; the fracturing and crushing of rocks ; (2) the trans- 



irt of their debris ; and (3) their apparent plasticity. 



Some further results show that the high pressures of 



line of the earlier experiments are not essential, but 

 that complete perforations can be obtained with pressures 

 of X 100 atmospheres. A cylinder of granite, cut in two 

 by a diametrical plane, and bound together with a 

 ligature of copper, was thus excavated along its whole 

 length by an irregular channel which opened on the 

 surface by two branches. In the case of a cylinder of 

 rock of which the height greatly exceeded the diameter 

 the perforation tended to the form of two cones united by 

 their summits. The action of the gases is not confined 

 to the drilling of the perforations, they have likewise 

 Ljrooved and striated the surfaces of the divisional planes 

 of the cylinders. These striations and groovings are not 

 produced, as might be supposed, and as M. Daubree 

 iiimself at first believed, by solid particles of rock carried 

 by the gas, and use as graving tools. It appears, in fact, 

 that the gases themselves are able to striate and groove 

 the rock on their first contact with it. 



As an interesting corollary to his experiments, M.' 

 Daubrde points out, that leakage from steam pipes may 

 in a similar way cut through metal plates. An example 

 IS quoted in which metal exposed to the escaping vapour 

 from a steam pipe (pressure, seven atmospheres) was 

 channelled and striated : the resulting marks were 

 similar to those of a saw or file. A valve on a steam 

 f)ipe, again, has been attacked in a similar way. 



All these groovings in the metal have received a similar 

 polish to that given by emery. 



In the experiments the gases have in general caused 

 the fusion of the surfaces which they have attacked. 

 Thus, on the surfaces of the divisional plane of a granite 

 > yhnder the felspar is melted into white globules forming 

 -iiall projections. The plates of mica have also been 



iltened. Even the quartz has not escaped, but appears 

 'Lted in a manner which recalls the erosion produced by 

 liydrofluoric acid. 



•Scales of the rock are detached by the very unequal 

 expansion as by a sort of shock. 



.\ black crust exactly similar to the crust of meteorites 



IS been produced with certain stones. 



The transport of the debris produced in the perforation 

 of the cylinders of rock is applied by M. Daubrde to the 

 history of certain cosmic dusts, and the sediments existing 

 in some of the deeper parts of the ocean. In making the 

 perforations the gases carry out a quantity of debris. A 

 Tirt of this was collected on sheets of cardboard covered 



■ th vaseline. The particles arrange themselves in con- 



ciUric circles on the sheet according totheirsize. Some 



of the large particles pierce the cardboard, and even its 



supporting plate ; the very fine particles are carried to a 



j distance by the gases, which they render opaque. In the 



( powder retained on the cardboard, two sorts of grains can 



I be distinguished under the microscope. The first are 



' indistinguishable from those produced by simple 



mechanical pulverisation; the second have a special 



NO. 1236, VOL. 48] 



character intimately connected with the particular con- 

 ditions of the experiment. 



Thus, in the case of granite, fragments of all three 

 constituents, quartz, felspar, and mica, are found in the 

 powder produced. But besides this, minute, perfect or 

 nearly perfect, spheres are found. These are opaque and 

 black, or slightly translucent and brownish, with a 

 glistening surface, and sometimes furnished with a very 

 characteristic neck. They are doubtless the products of 

 fusion. 



This latter part of the powder of erosion seems identical 

 with certain parts of the atmospheric dust, and that found 

 in the deeper ocean, as well as in geological formations 

 of various ages, and which have generally been looked 

 upon as of extra-terrestrial origin. Thus the conclusion 

 is arrived at that, while part of the so-called cosmic dust 

 is undoubtedly of extra terrestrial origin, the opening of 

 volcanic and other channels in the earth's crust by high- 

 pressure gas has also played an important part in its pro- 

 duction. 



Eruptive breccias may also have been produced by the 

 force of high-pressure gas, as shown by the fracturing, 

 breakingup, and reconsolidatingof the rocks experimented 

 upon. 



A more remarkable fact is the passing back of the 

 pounded and broken-up rock to its original solid state 

 under the influence of the same gaseous pressure. Thus 

 the fragments of the rock in the experiments were found 

 to have moulded themselves so exactly on the containing 

 steel apparatus as to have acquired a specular polish. 

 The rock had, moreover, taken the impress of striations 

 upon the steel. Limestone thus regenerated showed 

 a schistosity concentric with the cylinder. It seems 

 obvious, then, that the rocks of the earth's crust, having 

 so frequently been subjected to enormous pressure, and 

 so often folded and contorted, must in a similar way have 

 been broken up and regenerated. 



Another experiment showing the apparent plasticity of 

 rocks is as follows : — 



A cylinder of Carrara marble without a preliminary 

 fissure, but with furrows on one of the ends and on the 

 side, was placed in the apparatus and subjected to a pres- 

 sure of 2400 atmospheres. It was afterwards found to 

 be perforated with a channel, and moreover to be ac- 

 curately moulded on the containing apparatus so as to 

 take the impress of the concentric striations as in former 

 experiments. The furrows were completely effaced, while 

 the diameter of the cylinder was increased and its height 

 diminished. 



The ejection of rocky matter through the channels per- 

 forated by high-pressure gas occupies another paper. In 

 such high-pressure gas M. Daubree contends we have an 

 agent capable of accounting for the facts in conformity 

 with his experimental results. Special reference is made 

 to certain trachytic domes— as, for e.vample, those of the 

 high plateau of Quito — of which the form seems to in- 

 dicate that the rock matter forming them was ejected in 

 an almost solid state. These domes, M. Daubree sup- 

 poses, crown the summits of orifices (diatremes) opened 

 by the passage of high-pressure gas, and were themselves 

 afterwards forced out by the same pressure. Attention is 

 called to the remarkable uniformity in height observable 

 in groups of volcanoes. This is explained as the result 

 of origin from one common reservoir of pressure. The 

 height of the volcanic cone gives a measure of this pres- 

 sure. On the other hand, the hypothesis likewise ex- 

 plains the difference in height in different regions. Thus, 

 in certain cases, reduction of pressure would be effected 

 by lateral escape of gas, as happened in certain experi- 

 ments in spite of the utmost care. A similar reduction 

 of pressure may have occurred through the blocking of 

 the channels of egress of the gas. This, too, occurred in 

 certain of the experiments, notably when gypsum was the 

 rock experimented on. With this roclc the channel 



