SOURCES OF SODIUM CHLORIDE 367 



A large part of the salt of the Dead Sea is said to be derived 

 through leaching of an older salt bed. 



A far more important, because more universal, source of salt is 

 found in the imprisoned or connate waters of the older marine sedi- 

 ments. When sediments carrying such water are exposed by erosion, 

 their saline contents will be drawn to the surface by capillarity and 

 the evaporation of the water. It is obvious that this can proceed on 

 an extended scale only in arid districts, where meteoric waters play 

 but a minor part. The salt from the fossil sea water will form an 

 efflorescence on the surface of the rocks, where it will remain until 

 removed by the wind or rain. If the region is a drainless basin the 

 salt redissolved by the rain will be carried to the center of a neigh- 

 boring depression, where it will accumulate on evaporation of the 

 water. Salt carried by wind may be deposited anywhere within or 

 without the basin. 



The quantity of salt which is furnished by various ancient ma- 

 rine sediments depends to a large degree upon the pore space of the 

 rock. As we have seen (page 140), this is sometimes as high as 

 60% or over, but more generally falls below 40. If we take 35% 

 as an average measure, and take the salinity of the former ocean as 

 equal to that of to-day, i. c, 35 permille, we can readily see that 

 marine sediments include about 1% of sea salt, which is three- 

 fourths NaCl. A marine formation, which has a thickness of 1,000 

 meters, as in the case of the Jura of Europe, could furnish a bed of 

 salt approximately 10 meters thick and extendhig over the entire 

 area covered by such a formation. If such salt becomes concen- 

 trated into a smaller area, the deposit will, of course, be of a pro- 

 portionally greater thickness. 



Analyses of modern marine sediments have shown an even 

 greater salt content, due to electrolytic separation of the salt from 

 sea water. Thus the deep-sea red clay contained from 6.8 to 8% 

 of salt. Diatomaceous ooze contained 5.4% ; Antarctic glacial clay, 

 1.9 to 3-7%; Globigerina ooze, i.o to 3.4%. These differences in 

 amount are due to differences in absorption power of the various 

 sediments. ( Andree-2 :j55.) 



The leaching of the connate salts from old sediments furnishes 

 the rivers with their load of salt in solution ; as an example may be 

 quoted the high percentage of chlorine which rises to 32.63% in 

 the Rio de los Papagayos of Argentina. In this same river the 

 water carries 26.48% of sodium,* its total salinity being 9.185 per- 

 mille. This water runs into the ocean, but if similar water runs into 



* This percentage is of the total soHds, corresponding to 2.997 ^"d 2.432 

 permille, respectively. See table pp. 162-3. 



