December 8, 19 lo] 



NATURE 



173 



future in ameliorating the lot and uplifting the 

 coloured people, socially and morally. 



Although no one is more fully aware than Sir Harry 

 Johnston of the failings and moral weaknesses of the 

 negro, he takes a very hopeful view — which many 

 persons with a less intimate knowledge of the black 

 man may think unreasonably sanguine— of his future, 

 and especially of the hybrid's prospects, in the New 

 World, provided only that he follows the example and 

 teaching of his great and wise leader, Dr. Booker 

 Washington, who "'wants the negro to become the 

 most industrious race in the United States " (p. 407). 

 because only work will exhaust his energies and keep 

 him out of mischief. 



The book starts with a statement of Sir Harry 

 Johnston's views on the negro's place in nature, which 

 for the most part are well known to readers of his 

 >cher books. 



It is unfortunate, however, that on the very slender 

 basis of the evidence apfforded by the skeletons in the 

 Grimaldi caves (see p. 26) he extends the habitat of 



Fig. 2. — lype of Modern Xegro ; an electrical engineer trained 

 at Tuskegee. From " Ihe Negro in the New World." 



he negro over half the continent of Europe and the 

 whole of the British Isles ! 



It is not as a work of science, however, that this 

 Avork, with its introductory vulgarisation of anthro- 

 pology, is to be judged, but as a book of exceptional 

 interest, and as the reasoned judgment of a man of 

 wide experience on one of the most difficult socio- 

 logical problems of the present time. 



G. Elliot Smith. 



GEOLOGICAL CHRONOLOGY.^ 



T^HE vexed question of the age of the earth has 

 *• passed through several distinct phases. Lyell 

 arid his contemporaries, accustomed to dwell on the 

 extreme slowness of geological processes, considered 

 themselves free to make unlimited "drafts on the 



1 ■' A Preliminary Study of Chemical Denudation." By F. W. Clarke. 

 Pp. 19. Smithsonian Miscellaneous Collections, vol. Ivi., No. 5. (Wash- 

 ington, 1910.) 



"The Age of the Earth." By G. F. Becker. Pp.28. /W</., vol. Ivi., 

 No. 6. (Washington, 1910.) 



NO. 2145, VOL. 85] 



Dank of lime"; but, since 1862, this position has been 

 seriously challenged from the physical side. The 

 chief argument brought against it was that, granting 

 the globe to have cooled from a molten state, it would 

 attain its assumed present thermal condition in a few 

 scores of millions of years, only a fraction of which 

 time would be available for the stratigraphical record. 

 If the general body of geologists, influenced by the 

 high authority of Lord Kelvin, have tried to adapt 

 themselves to this narrow limitation, it has not been 

 without reluctance, and some sturdy dissentients have 

 refused any such coercion. To these, during the last 

 few years, welcome support has come from unexpected 

 quarters. The nebular hypothesis of the earth's 

 origin, upon which the estimates of Kelvin and King 

 were tacitly based, has been shaken by Moulton's 

 calculations and other arguments put forward by 

 Chamberlin. Moreover, the remarkable discoveries in 

 the domain of radio-activity have compelled a recon- 

 sideration of the thermal state of the globe. Estimates 

 of the earth's age deduced from its supposed rate of 

 cooling clearly become futile if we have no good reason 

 for believing that the earth is a cooling body. On 

 the other hand, from the radio-active properties of 

 various minerals Strutt has deduced geological ages 

 liberal enough for the most extreme uniformitarian. 



The debate concerning the age of the earth is thus 

 no longer an issue between geologists and physicists, 

 since the newer school of physics has declared on the 

 side of the ampler chronology. Meanwhile, there has 

 arisen within the body of geologists a formidable 

 minoritv who contend, on geological grounds, for an 

 estimate of geological time no more elastic than that 

 imposed bv the old argument from refrigeration. The 

 discussion has followed two distinct lines, starting on 

 one hand from the rate of accumulation of sedi- 

 ments, and on the other from the rate at which 

 sodium is carried down bv rivers into the sea. The 

 interesting memoirs by Mr. Clarke and Dr. Becker, 

 recently published by the Smithsonian Institution, 

 deal mainly with the second mode of approaching the 

 problem, but Becker offers also a revised estimate of 

 the earth's age as calculated from the rate of cooling. 



In 1899 Prof. Joly made estimates, first, of the 

 total amount of sodium contained in the ocean, and, 

 secondly, of the amount annuallv carried down by 

 rivers, and, dividing the one by the other, obtained 

 the quotient 97,600,000 3ears as the age of the ocean, 

 supposed to be initially of fresh water. If the sea 

 contained some salt from the beginning", this figure 

 must be reduced accordingly. The choice of sodium 

 is dictated bv the consideration that this constituent is 

 less removed from sea-water than any other. A 

 relatively small correction is made for salt carried 

 inland by the wind, and it is assumed that there is no 

 other process of importance by which sodium is being 

 continually removed from the oceanic waters. We 

 mav note in passing that certain observed facts, such 

 as the evident chemical action of sea-water upon 

 potash-granites, throw some doubt upon this assump- 

 tion. 



The data at Joly's command were very defective, 

 and the main object of Clarke's memoir is to revise 

 the calculation in the light of more recent information. 

 In particular he has drawn upon the large mass of 

 observations relative to the discharge, drainage-areas, 

 and salinity of American rivers contained in the Water- 

 Supplv Papers of the United States Geological Survey. 

 He has brought tosfether the available information on 

 the same points for other parts of the world, and 

 indicated where additional observations are especially 

 desirable. The "denudation factor," i.e. the number 

 of metric tons annually removed in solution from 

 each square mile of a drainage-basin, varies from 

 105 for the St. Lawrence to 16 for the Nile, and the 



