Vol. 65.] ANNIVERSARY ADDRESS OE THE PRESIDENT. XCvii 



by this possibility as to have imagined that some inland lakes, 

 like the Dead Sea for instance, may have received their supplies 

 of salt from the winds. 1 



"We are fortunate in possessing some very precise information on 

 this subject. In England, according to Sir Archibald Geikie, the 

 mean amount of chlorine present in rain-water is 2*2 parts per 

 million. But it is to the United States that we must again turn 

 for the most systematic investigation. The amount of chlorine in 

 the rainfall has been determined at a large number of stations 

 distributed over the eastern maritime provinces, between lat. 40° 

 and 47° N. and from the coast to about 350 miles inland. The 

 results have been plotted on the map (fig. 2, p. xcviii) by curves 

 known as isochlors. These run approximately parallel to the 

 coast : the outermost curve, representing 6 parts of chlorine per 

 million of water, is rapidly succeeded by the isochlors 5, 4, 3, 

 and 2 ; the spacing then becomes wider till the isochlor of - 2 

 is reached. It cuts the north-western extremity of Lake Erie ; 

 beyond the Ohio the air is free from salt. 2 



Nevertheless, as we proceed westwards beyond the Ohio, there 

 is no falling-off in the amount of sodium-chloride contained in the 

 river-water ; on the contrary, it increases, as is particularly well 

 shown by the western tributaries of the Mississippi. This salt 

 does not come from the rain, and we must seek for it in the soil. 

 Salt-bearing Trias, however, is known to extend from the eastern 

 base of the Canadian Rockies to New Mexico, and it occurs in the 

 Black Hills of South Dacota. These feed the western tributaries, 

 and the Red River owes its colour to Trias marls or clays. The 

 salt of these deposits is certainly not an immediate result of 



1 Posepny, 'Zur Genesis der Salzablagerung &c.' SB. Wien. Ak. math.- 

 naturw. Kl. vol. lxxvi (1877) Abth. i, p. 179. (In connexion with this, see 

 E. Tietze, 'Zur Theorie der Entstehung der Salzsteppen, &c.' JB. k.-k. Geol. 

 Beichsanst. Wien, vol. xxvii, 1877, p. 341 ; and Muntz, ' Sur la Kepartition du 

 Sel Marin suivant les Altitudes ' C. E. Acad. Sci. Paris, vol. cxii, 1891, p. 447.) 



W. Ackroyd, 'On the Circulation of Salt & its Bearing on Chemico- 

 geological Problems, more especially the Age of the Earth ' Chern. News, 

 vol. lxxxiii (1901) pp. 265-268; id., 'On the Circulation of Salt in its 

 Eelations to Geology' Geol. Mag. dec. 4, vol. viii (1901) pp. 445-469 & 558- 

 559; id., 'The Circulation of Salt, &c.' Proc. Yorks. Geol. & Polytech. Soc. 

 vol. xiv (1901) pp. 401-421 ; and a reply by J. Joly, ' Circulation of Salt, &c.' 

 Geol. Mag. tern. cit. pp. 504-506. 



2 Jackson, Water-Supply & Irrigation Paper, No. 144, U.S. Geol. Surv. 

 1905. The chlorine in the atmosphere did not escape the notice of Prof. Joly, 

 who made the ample allowance of 10 per cent, for it in his estimate. 



