136 



♦ KNOWLEDGE ♦ 



[Aphh, 1, 1887. 



millions have come from the many millions of suns in our 

 galaxy during the many millions of years of their sunlike 

 existence. But the giant planets were once suns, and in 

 their sunlike state, which must have lasted millions of 

 yeiirs, they must have ejected their smaller comets and 

 meteor systems, which even now after millions of years have 

 paths passing near the orbits of their parent orbs. Our 

 earth and her fellow terrestrial planets had their sunlike 

 stage of life, too, and it must have been while the earth was 

 a sun that the meteors explained specially by Tschermak's 

 theory were expelled. 



All the known facts correspond with the general theory 

 thus pre,sented ; nor can any fact be noted which even intro- 

 duces a difficulty, though of coiu-se it is very easy, as some 

 astronomers in America have recently shown, to point out 

 that comets and meteors whose interpretation belongs to 

 one part of my theory cannot be well explained if we try to 

 interpret them by another part. 



Lastly the only sunlike body we can study, our own 

 sun, has been caught in the very work of ejection which 

 this theory assigns to sunlike bodies. 



THE ORIGIN OF MOUNTAINS.* 



3HE " delightful uncertainty of science " forms 

 one of its chief charms to the candid mind, 

 as the absolute iixity of dogma forms its 

 main recommendation to stupidly conserva- 

 tive and unprogressive intellects. Dull 

 people like to be told a thing once for all, 

 and to stick to it thenceforth and for ever 

 with a Chinese invariability, an immovable 

 stolidity as of the Medes and Persians. Intelligent people 

 modify their opinions in accordance with new facts or new 

 aspects of events as soon as these are brought to their notice. 

 Geology (on its dynamic side at least) is still to a great 

 extent in that plastic stage where great modifications may 

 yet be expected, and where a corresponding modifiability 

 of opinion is therefore most necessary to every student. 

 Mr. Mellard Reade's book on the origin of mountains is a 

 splendid examp'e of the sort of shaking our preconceived 

 ideas may any day suffer. We do not say he has entirely 

 upset all our current notions about the growth of mountain 

 i-anges ; we must wait to assert that tUl his theory has 

 been thoroughly sifted and debated and fought over, as it 

 will be, by all the competent specialists in his chosen science. 

 But we do say he has administered a rousing dose of vigorous 

 scepticism, and submitted the accepted theory on the subject 

 to a powerful solvent, which leaves us at least in an attitude 

 of suspended judgment, with a distinct inclination towards 

 Air. Eeade's own way of thinking. 



The theory of the origin of mountain chains at present in 

 vogue — the theory more or less supported, hypothetically at 

 least, by the great names of Lyell and Geikie — refers them 

 in the last resort to tangential strains, regarding them 

 essentially as ridges due to the compression induced in the 

 rigid outer crust of the globe by a shrinkage of the heated 

 nucleus within. This theory Mr. Reade subjects to a very 

 thorough and crushing criticism. He insists upon applying 

 to it strict arithmetical and mathematical tests, and shows, 

 we venture to believe, most surprising flaws in the reasoning 

 by which it has hitherto been sustained. Briefly put, the 

 result of his investigation, on the destructive side, is to prove 

 that no shrinkage sufficient for the purpose exists, and that 

 the greatest conceivable shrinkage would be quite inadequate 



» " The Origin of Mountain Ranges." By T. Mellard Reade, C.E. 

 (London : Taylor & Francis. 1886.) 



for the production of the effects ordinal ily attributed to it. 

 The leasoning in this controversial portion of his work, 

 however, is so close and condensed that it hardly admits of 

 presentation in a brief summary. Readers must turn for 

 information to the work itself. On the constructive side, 

 Mr. Reade opposes to the orthodox theory a new and most 

 plausible hypothesis of his own. He begins by showing 

 that periods of great sedimentary deposit precede the birth 

 of every large mountain chain. Now Babbage proved long 

 ago that an addition of sediment to any part of the earth's 

 crust must raise the temperature of the subjacent mass 

 which it covers and encumbers. The " isogeotherm " or 

 line of equal temperature will therefore rise, and by a series 

 of reactions, which Mr. Reade describes in full detail, will 

 produce immediate results by expanding the new sedimen- 

 taries in every possible direction. But the tendency to 

 expand horizontally is checked, of course, by the rigid mass 

 of the earth's crust bounding the locally heated area. The 

 heated area is, therefore, forced to expand vertically alone, 

 and to form those ridging-ups of the surface which we 

 know as mountain ranges. Mr. Reade, being himself a 

 civil engineer of considerable experience, has experimentally 

 determined the mechanical efl'ects of expansion by heat on 

 bars of various sandstones, marbles, and other like mate- 

 lials, and has proved that stone does actually ridge up 

 under such circumstances so as to produce miniature moun- 

 tain ranges. Being also an accomplished geologist, he has 

 applied his theory to the explanation of large classes of 

 facts in dynamical geology ; he accounts for the foldings of 

 strata, the repacking of beds, and the production of faults, 

 in a way which is certainly ingenious and appears to possess 

 much plausibility as well. The thing hangs together with 

 notable verisimilitude. His whole theory, indeed, pro- 

 ceeds upon the now familiar line of puiutiug out the vast 

 cumulative effects of comparatively small and unobtrusive 

 factors. As an example of the quantitative efl'ect of a rise 

 of temperature in a given area and depth of rock he takes a 

 district of five hundred miles in length by five hundred in 

 breadth. The crust to a depth of twenty miles beneath 

 this comparatively small district would comprise five 

 million cubic miles of rocky material. If this mass 

 were heated to a mean of 1,000° Fahr. — a temperature 

 which, says Mr. Reade, must have occurred over and over 

 again in the local heating of the earth's crust — there would 

 be an increase of volume to the extent of 52,135 cubic 

 miles, which excess must necessarily rise in the arched or 

 vaulted form of a mountain chain. Enormous as this result 

 may appear at first sight, the block of crust here postulated 

 is nevertheless only the j.yl^^Tf pai't of the solid matter of 

 the whole globe. The mountain chain thus produced would 

 be indeed but a very insignificant one ; the vast masses of 

 sedimentary deposit out of which have been formed and 

 carved the Alps, the Andes, the Rocky Mountains, and the 

 Himalayas are spread out over enormously larger and wider 

 areas. The greatest of mountain ranges indeed are but 

 trifling excrescences upon the outer surface of our third-rate 

 planet. 



It would be premature to pronounce dogmatically upon 

 the truth or error of Mr. Reade's startling hypotheses. 

 They must be tested by time, and verified or disproved by 

 the long and careful observations of working geologists. 

 But whether true or not, there can be no doubt at all of 

 their fundamental importance, their singular originality, 

 their admirable elaboration, and the skill and ability with 

 which they have been worked out and presented to our 

 minds. His doctrine, in fact, is simply revolutionary. If 

 he succeeds in convincing others, he will have altered our 

 entire conception of dynamical geology. If he does not 

 succeed, he will at least have aroused a wholesome scepticism 



