Apbil 1, 1910] 



SCIENCE 



509 



ences," by E. C. Archibald ; " Notes " ; " New 

 Publications." 



The April number of the Bulletin contains : 

 " Simon Newcomb," by E. W. Brown ; " A 

 new proof of Weierstrass's theorem concern- 

 ing the factorization of a power series," by 

 G. A. Bliss ; " On some theorems in the Lie 

 theory," by L. D. Ames ; " On the diseontin- 

 mous ^-groups defined by rational normal 

 curves in a space of n dimensions," by J. W. 

 Young ; " A new analytical expression for the 

 number tt, and some historical considerations," 

 by G. Vacca; Eeview of Hermite's Works, 

 Volume II., by James Pierpont ; " Shorter 

 notices " : Serret-Scheffers, Differential- und 

 Integralrechnung, third edition, Volume III., 

 by A. E. Crathorne; Eichter's Kreis und 

 Kugel in senkrechter Projection, by D. D. 

 Leib; Granville's Plane and Spherical Trig- 

 onometry, by Jacob Westlund; Lecornu's 

 Dynamique appliquee and Boulanger's Hy- 

 draulique generale, by J. B. Shaw; Schaf- 

 heitlin's Besselsche Funktionen, by A. E. 

 Crathorne. Correction ; " Notes " ; and " New 

 Publications." 



^ REFLECTIONS ON JOLY'S METHOD OF 

 DETERMINING THE OCEAN'S AGE 



As is well known to all geologists, the very 

 important method of estimating the age of 

 the ocean devised by Mr. J. Joly consists sub- 

 stantially in dividing the total sodium content 

 of the sea water by the yearly contribution 

 from the land, this annual tribute being ascer- 

 tained by analyzing river waters and gauging 

 the streams. It is assumed on uniformitarian 

 principles that what variation there has been 

 in the annual salt tribute is undiscoverable.^ 

 In a long-forgotten memoir Edmund Halley^ 

 made a very similar suggestion and antici- 

 pated Lyell in propounding a strictly uniform- 

 itarian doctrine of the accumulation of salt. 



Oceanic sodium is at least chiefly derived 

 from lime-soda feldspars, which as essential 

 constituents are practically confined to Arch- 



^ Trans. R. S. Dublin, Vol. 7, 1899, p. 23, and 

 Brit. Assoc. Eep., 1900, p. 369. 



' Science, Vol. XXXI., March 25, 1910, p. 459, 

 and Phil. Trans., Vol. 29, 1715, p. 296. 



ean and later igneous rocks. The original 

 surface of the earth must have consisted of 

 such rocks to the exclusion of all others, while 

 at the present day the greater part of the land 

 area is covered with sedimentaries. Now the 

 rate of decomposition of rocks is chiefly de- 

 pendent on exposure. Even in areas of an- 

 cient feldspathic massives decomposition does 

 not seem to penetrate to great depths. Thus 

 in the southern Appalachians great areas of 

 gneiss and allied rocks are now covered by a 

 blanket of saprolite (rotten rock in place) 

 which is in many localities 50 feet in thick- 

 ness, but at all the points where I have ob- 

 served it less than 100 feet thick. Immedi- 

 ately below the saprolite blanket there is 

 incipient decomposition and the feldspars are 

 milky, but not many yards lower down the 

 feldspars are characteristically translucent and 

 the rock bluish in tint. A layer of decompo- 

 sition products 100 feet thick seems to arrest 

 decay. Corresponding statements are true of 

 Tertiary volcanics excepting where the decom- 

 position is soLfataric. On the other hand 

 Mesozoic and Paleozoic massive rocks deeply 

 buried under sediments are not seldom found 

 to be very free from decomposition. In short, 

 buried massives decompose at a rate which is 

 scarcely sensible. 



It is quite conceivable that in the far distant 

 future all the massive rocks might be thor- 

 oughly decomposed down to sea level or a trifle 

 below. The continents would then be exclu- 

 sively detrital. Under such conditions there 

 could be no further important additions to the 

 sodium content of the ocean, for there would 

 then be no leaching, while mere diffusion to 

 any considerable distance is too inordinately 

 slow to produce any noteworthy result even in 

 millions of years. 



Thus in the distant past there must have 

 been a time when a far greater mass of mas- 

 sive rock was decomposed each year than now 

 decays in the same period; and a limit to this 

 process can also be foreseen. The total area of 

 exposed massives has surely diminished and 

 will continue to diminish. Climate and tem- 

 perature may perhaps have been in the past 

 much what they are to-day; the rate of chem- 



