September 3, 1914] 



NATURE 



logical evidence from any part of the world has the 

 same value as that obtained in the little continent 

 which has been the most prolific in the products of 

 nomenclature and the most productive in text-books. 



Since the days of Charles L3ell no geologist has 

 been so conspicuously successful in analysing the 

 accumulated mass of evidence, in bringing together 

 the essential facts from all hands, and in compensat- 

 ing for the local excesses of literature. Only those of 

 us who, by long absence from Europe, have felt the 

 full disadvantages of having to express our thoughts 

 in alien terminology can appreciate the real value of 

 Suess's great work. His death since our last meeting 

 makes a conspicuous mark in the history of geological 

 science. 



A meeting of the British Association in Australia 

 brings home forcibly to the members of Section C 

 the fact that British Imperial geology is really "the 

 science of the earth " ; partly for this reason one feels 

 inclined to get outside the science and take a sur\'ey 

 of some of its suburbs. Not many of them have been 

 left untraversed by my distinguished predecessors in 

 this chair ; but there has been of recent years a ten- 

 dency to avoid the inner earth, which has rightly 

 been described as "the inalienable playground of the 

 imagination," and consequently, therefore, common 

 land to the geologist as well as the geodesist, physicist, 

 and mathematician. 



The geologist who looks below the purely super- 

 ficial phenomena of the crust is generally regarded as 

 straying beyond his province ; but the desire to see the 

 birth certificate of seme of the strange and often un- 

 acceptable "causes" which the mathematical physicist 

 offers us is a pardonable form of curiosity. Our ideas 

 regarding intra-telluric conditions are even proving to 

 be of economic value, one of the most recent and 

 unexpected results of the kind being that just estab- 

 lished by Baron von Eotvos in Hungary,* whose pre- 

 dictions now bid fair to outstrip those of the 

 "diviner"! Having noticed the low gravity values 

 over the great cores of rock-salt in the Transylvanian 

 " Schlier," he finds similar defects of gravity in the 

 same region over certain of the Sarmatian and Pon- 

 tian domes, which probably owe their shape to sub- 

 terranean salt-plugs and are now found to be great 

 storehouses of natural gas, which, with or without 

 liquid petroleum, is commonly found with the saline 

 "Mediterranean' facies of the Upper Tertiary in 

 Eastern Europe. Baron von Eotvos also finds that on 

 the eastern margin of the Great Hungarian Plain, 

 where the younger Tertiary beds are completely con- 

 cealed by a mantle of alluvium, mud-volcanoes and 

 gas-springs are sometimes found in areas of marked 

 gravity defect, and some of these are now also being 

 drilled for natural gas. 



When our ideas of the state of affairs below the 

 surface thus begin to yield economic results, there is 

 hope that they are at last steadying down, becoming 

 more settled, and indeed more "scientific." It may 

 not be unprofitable, therefore, to review some of the 

 advances recently made in developing theoretical con- 

 ceptions regarding the interior of the earth that are 

 of direct importance to geologists. In undertaking 

 this review I am conscious of the fact that I shall be 

 traversing ground that is generally familiar to all, 

 and much of it the special property of specialists 

 whose views I hesitate to summarise and should not 

 dare to criticise. As the author of the " Ingoldsby 

 Legends" said of the only story that Mrs. Peters 

 would allow her husband to finish, "The subject, I 

 fear me, is not over new, but will remind my friends — 



" Of something better they have seen before." 



J Comptts rendus, XVIIeme Conf. de I'Assoc. Giod^s. Intemat. Ham- 

 burg, 1912, pp. ^2T, 437. 



The intensity and quantity of polemical literature on 

 scientific problems frequently varies inversely as the 

 number of direct observations on which the discussions 

 are based : the number and variety of theories con- 

 cerning a subject thus often form a coefficient of our 

 ignorance. Beyond the superficial observations, direct 

 and indirect, made by geologists, not extending below 

 about one two-hundredth of the earth's radius, we 

 have to trust to the deductions of mathematicians for 

 our ideas regarding the interior of the earth ; and they 

 have provided us successively with every permutation 

 and combination possible of the three physical states 

 of matter— solid, liquid, and gaseous. 



Starting, say, two centuries back with the astrono- 

 mer Halley, geologists were presented with a globe of 

 which the shell rotated at a rate different from that of its 

 core. In more recent times this idea has been revived 

 by Sir F. J. Evans (1878) to account for the secular 

 variations in the declination of the magnetic needle. 

 Clairault's celebrated theorem (1743J, on which 

 Laplace based the most long-lived among many cos- 

 mogonies, gave us a globe of molten matter sur- 

 rounded by a solid crust. Hopkins demanded a globe 

 solid to the core, and, though his arguments were 

 considered to be unsound, his conclusions have been 

 revived on other grounds; while the high rigidity of 

 the earth as a body has been maintained by Lord 

 Kelvin, Sir George Darwin, Prof. Newcomb, Dr. 

 Rudski, and especially by the recent observations of 

 Dr. O. Hecker, supplemented by the mathematical 

 reasoning of Prof. A. E. H. Love. Hennessy (1886), 

 however, concluded that the astronomical demands 

 could be satisfied by the old-fashioned molten earth 

 in whicii the heavier substances conformed to the 

 equatorial belt. 



As long ago as 1858 Herbert Spencer suggested 

 that, on account of its temperature being probably 

 above the critical temperature of known elements, 

 the centre of the earth is possibly gaseous. Late in 

 the seventies Dr. Ritter revived the idea of a gaseous 

 core surrounded by a solid crust, and this was modified 

 in 1900 by the Swedish philosopher, Svante Arrhenius, 

 whose globe with a solid crust, liquid substratum, and 

 gaseous core is now a favourite among some geo- 

 logists. 



Wiechert (1897) supposed that the core of the earth, 

 some 5,000 kilometres in radius, is composed mostly 

 of iron with a density of 7-8, while this is surrounded 

 by a shell of lithoidal material having a density of 

 about 30 to 34 ; and this great contrast in density is 

 about that which distinguishes the iron meteorites 

 generally from those of the stony class. Arrhenius 

 also assumes that iron forms the main part of the 

 central three-quarters, and he shows that this distri- 

 bution of substance may still be consistent with his 

 theory of a gaseous core ; indeed, he not only imagines 

 that the whole of the iron nucleus is gaseous, but 

 also most of the siliceous shell, for he leaves only 5 

 per cent, of the radius as the depth of the solid and 

 liquid shells combined. 



But the variety of ideas does not end with theories 



on the present constitution of the globe. Poisson 



required the process of solidification to begin from 



the centre and to progress outwards, while other 



mathematicians had been happy with the Leibnitzian 



consistentior stains as the first external slagg\- crust. 



Since the days of Laplace all naturalists have been 



I forced to accept the idea of a solar system formed by 



j the cooling and condensation of a spheroidal gaseous 



I nebula ; and all except those geologists who have 



I vainly searched for traces of the primeval crust have 



I been happy in this belief. 



Recently, however. Dr. F. R. Moulton and Prof. 

 T. C. Chamberlin in America have brought together 

 arguments from different points of view to construct 



NO. 2340, VOL. 94] 



