236 



NATURE 



[July 5, 1900 



kindred sciences to attain the solution of a problem so fascinat- 

 ing. It is true that past efforts in this direction have taught us 

 to expect at the best a merely approximate result, by whatever 

 method this problem may be attacked ; at the same time, every 

 attempt is welcome which shall tend to more narrowly limit the 

 margin of approximation. In the important treatise before us. 

 Prof. Joly proposes a novel and ingenious method of approach- 

 ing this difficult question, and if his argument relies for its suc- 

 cess on a considerable basis of assumption, he has nevertheless 

 arrived at results of striking interest. 



It is, first of all, assumed that the denudation by solution of 

 the land surface, since the first formation of a solid earth-crust, 

 has been on the whole a uniform process ; and further, that the 

 amount of sodium now contained in the ocean has been for the 

 most part transported to it by rivers since the land surface first 

 became exposed to the action of solvent denudation. The 

 reasons which, in the author's view, render these assumptions 

 probable truths are fully discussed in the paper. If, now, we can 

 obtain a correct estimate of the amount of sodium at present 

 contained in the waters of the ocean, and also of the amount 

 annually supplied to the latter by rivers, we have the requisite 

 data whereby the earth's geological age may be determined. 

 Basing his calculations upon the most careful and recent esti- 

 mates. Prof. Joly finds that the mass of sodium contained in the 

 ocean amounts to IS, 627 x !&''■ tons. In estimating the amount 

 of sodium carried annually by rivers into the sea. Sir John 

 Murray's analyses of nineteen rivers (including many principal 

 ones) are quoted, and a result of 24,106 tons of sodium per cubic 

 mile of river water is obtained. Sir John Murray's estimate of 

 the annual river discharge into the ocean, amounting to 6,524 

 cubic miles, is also accepted. From these figures the mass of 

 sodium annually carried to the sea is calculated, and this amount 

 divided into the total mass of sodium contained in the ocean, 

 gives a result of about 94,800,000 years, representing the dura- 

 tion of geological denudation. So much is set forth in the first 

 section of the paper. In the succeeding eight sections correc- 

 tions on the above estimate are discussed, and several possible 

 objections are dealt with. 



The author first enters into a speculative discussion regarding 

 the succession of events attendant on the first cooling of the 

 earth's surface, with the object of arriving at conclusions as to the 

 nature of the primitive ocean. Incidentally the view is favoured 

 which supposes that at the first condensation of water upon the 

 surface a greater density was conferred on the sub-oceanic crust 

 than on the sub-aerial tracts ; it is deemed improbable that this 

 distribution of pressure became subsequently seriously modified, 

 and the author gives his support to a belief in the permanency 

 of ocean basins. The early ocean itself is supposed "for want 

 of other known alternative," to have contained " a quantity of 

 hydrochloric acid roughly represented by the chlorine now in 

 the ocean." This being admitted, it is clear that a certain 

 degree of saltness would primarily be acquired by the early 

 hydrosphere, and this must be allowed for in modifying the 

 above estimate of geological time. To accomplish this Prof. 

 Joly first quotes Clarke's average analysis, showing the probable 

 composition of the primitive earth-crust. The action of the 

 heated acid ocean upon such a rock mass, and the apportioning 

 of the acid among the bases, is next considered. It is calculated 

 that of the total amount of chlorine contained in the original 

 ocean, only 14 per cent, could have been taken up to form 

 sodium chloride, and in order to arrive at the actual amount of 

 this first formed sodium chloride, Prof. Joly proceeds to estimate 

 the chlorine of the original ocean. This is done by subtracting 

 from the total amount of chlorine now contained in the ocean 

 the quantity of that element supposed to have been transported 

 to it by rivers during the course of geological time. But of the 

 river-transported chlorine a certain proportion has been derived 

 from the sea itself, and for this a deductive allowance of 10 per 

 cent, is made as probal)ly sufficient. Having esimated that a 

 total of about 76 x 10" tons of chlorine are annually supplied by 

 rivers to the sea, the author assumes the duration of geological 

 denudation to have been about 86 x 10" years, and finds that 

 during this period 6536 x 10^'- tons of chlorine have been intro- 

 duced into the ocean. By subtracting this from the total 

 chlorine now contained in the sea (as sodium chloride and mag- 

 nesium chloride), a total of 21,780 x 10^- tons is arrived at, repre- 

 senting the original chlorine of the oceanic waters. If 14 per cent. 

 of this would unite with sodium, then 1972 x 10"- tons of sodium 

 were brought into solution by the action of the primitive acid 

 ocean. This result can now be employed in correcting the 

 original estimate of geological time, which was reckoned on the 

 NO. 1601, VOL. 62] 



supposition that all the sodium now in the ocean had been sup- 

 plied by rivers. Thu«, the total amount of sodium supplied by 

 rivers is reduced to 13,655 x lo'-' tons, and this deductive cor- 

 rection of i2-6 per cent, reduces the duration of geological time 

 to 86'9 x 10^ years. The value of this ingenious correction ap- 

 pears to be lessened, however, by the necessary introduction of 

 an arbitrary assumption for the duration of geological time. Is 

 there any reason, too, to show that at the first condensation of 

 water upon the earth, alkalies may not have been present to 

 neutralise to almost any unknown extent the acid of the primae- 

 val ocean ? The author believes that the amount of correction 

 necessary in allowing for the action of acids other than hydro- 

 chloric, in the primitive ocean, is practically negligible. 



By a further slight modification of the figures representing the 

 sodium annually transported into the sea, a final estimate of 

 89*3,000,000 years'is arrived at, a figure based, we are told, 

 " on the most complete estimate of probabilities." But even in 

 this estimate the author does not claim a degree of accuracy 

 "approximating to so small a time interval as 100,000 years." 



Prof. Joly then examines the significance of rock-salt de- 

 posits, as possessing a possible bearing on his theory, but having 

 discussed the origin of such deposits he concludes that any error 

 involved by ignoring them must be very slight. But the extent 

 of the saline deposits surely cannot possibly be estimated, and 

 may perhaps have been considerably underrated. Even if it be 

 admitted, as urged by the author, that the salt basins of the 

 present day are in great part not of oceanic origin, this does not 

 necessarily apply in like degree to saline deposits of the past, 

 when earth movements may have played a more vigorous part 

 in aiding their formation as oceanic derivatives. 



A point of seemingly great significance in its bearing on Prof. 

 Joly's theory is the retention of salts in the interstices of strati- 

 fied rocks, the salts derived from the waters in which the rocks 

 were laid down. In 1856 Dr. Sorby drew attention to the 

 soluble salts contained in certain dolomites, and Dr. Sterry 

 Hunt has recently referred to the " fossil sea water " retained in 

 the pores of stratified rocks. 



The observations of the Rev. O. Fisher on this point, 

 recorded in a recent review of Prof. Joly's paper ^Geol. Mag., 

 March 1900) are of the greatest interest, as showing that some 

 of the sodium of river waters may have been derived not from 

 the rocks, but originally from the ocean itself.^ In estimating 

 the mass of sodium held in solution by the ocean, should not 

 some allowance be made too for an unknown bulk of highly 

 pervious deep-sea sediments ? May not such deposits be in part 

 of great thickness, and by reason of the sea water with which 

 they are impregnated form a store for sodium ? 



In the succeeding section the potash and soda percentages Oi 

 the igneous and sedimentary rocks respectively are considered. 

 Quoting Clarke and Rosenbusch for estimates of these. Prof, 

 Joly attempts to prove that the deficiency of soda in the sedi- 

 mentary rocks (i"47 per cent, of soda and 249 per cent, of 

 potash, as against 3 '61 per cent, of soda and 2-83 per. cent, of 

 potash in the primitive crust) is accounted for by the amount of 

 sodium calculated to have been supplied to the ocean by rivers. 

 It is claimed "that the estimated amount of sedimentary strata 

 would, in its formation, be adequate to yield to the ocean the 

 sodium that is in it, assuming these sedimentaries to be derived 

 from rocks having the mean composition of the important erup- 

 tive masses now known." Allowance is made for a slight 

 deficiency in the sodium of the ocean by the existence of the 

 rock-salt deposits. For the success of this argument it is un- 

 fortunately necessary to assume that a correct estimate of the 

 total bulk of the sedimentary rocks is possible. Mr. Mellard 

 Reade's calculation is provisionally taken as a basis. Accepting 

 also Mr. Reade's estimate of the proportion of calcareous to 

 other sediments, the latter are found to be equal to a layer i'6 

 miles in depth over all the land area. From this the mass of 

 the detrital sediments is calculated, and the actual amount of 

 their soda is arrived at. To this is now added the amount of 

 sodium (reckoned as soda) contained in the sea. This restora- 

 tion would bring the soda percentage of the total mass of sedi- 

 mentary rocks, even allowing for the rock-salt deposits, to little 

 above 3 per cent., and in order that the figures shall be brought 

 into better accordance with Clarke's calculated soda percentage 

 for the primitive crust, the estimate of the amount of detrital 

 sedimentary rocks is ingeniously amended to equal a layer I'l 

 miles thick over all the land area, with the result that an amount 



1 Since these lines were written. Prof. Joly has dealt further with this 

 point and with the question of alkalies neutralising the primitive acid 

 ocean (Geol. Mag., May 1900). 



