52 PKOF. EDWAED HCLL, LL.D., P.K.S., F.G.S., ON 



16 From the above results of the analysis of various waters, 

 it will be seen that there is no essential difterence between 

 the waters of the ocean and those of lakes and rivers 

 except in the proportions of the dissolved ingredients. 

 There are, of course, occasionally substances specially abun- 

 dant, as is the case with bromine in the waters of the Dead 

 Sea, probably derived from the volcanic district on its 

 borders; on the other hand, silica (Si O2), Avhich is not 

 mentioned in the waters of the Atlantic Ocean in the 

 analysis of Von Bibra, is certainly present in those waters, 

 and supplies the material from which sponges, diatoms, and 

 radiolaria build up their skeletons. It will be observed also 

 that chlorine and sulphuric acid is present in all the waters, 

 and these gases uniting with the alkalies, give lise to the 

 salts which are so abundant in the waters of the ocean and 

 of closed lakes. 



17 In considering the manner in which springs and surface 

 waters have become impregnated with salts and carbonates, 

 Ave have to recollect that all rocks decompose in presence of 

 the atmosphere. This is mainly due to the carbonic acid 

 (carbon-dioxide) contained in the air and rain Avater, which 

 acts upon felspathic rocks, composed, as Ave have seen, of 

 double silicates of alumina, potash, and soda. Ebelmau has 

 well explained the process by Avhich basaltic and similar rocks 

 are decomposed under the influence of the atmosphere. 

 The carbonic acid (carbon-dioxide) combines Avith the lime 

 and magnesia, while the silica is liberated in a soluble 

 form. The felspar is more stable than the pyroxene and 

 hornblende, but it idtimately gives way, forming a hydrous 

 silicate of alumina. Thus Ave can account for the presence 

 of carbonates of lime and magnesia, free silica, and by a 

 further process in presence of sulphuric acid and chlorine of 

 the A^arious sulphates and chlorides. 



18 NoAv. as bearing on the fact of sodium chloride (or com- 

 mon salt) being the chief ingredient in oceanic Avaters, as 

 well as in those of the Dead Sea and most salt lakes, we 

 must recollect that the soda-felspars are much more soluble 

 than the potash-felspars, and on this account Ave have pro- 

 bably a true cause of the predominance of sodium chloride. 

 The rocks composed in the main of such felspars as labra- 

 dorite, albite, oligoclase, and andesine, Avere therefore more 

 poAverfully acted upon than those composed of orthoclase 

 and sanidine ; but even in these cases many orthoclase 

 granites contain proportionate quantities of the soda felspars 



