208 



KNOWLEDGE. 



[September 1, 1890. 



Such model oceans are especially abundant on " the 

 Roof of the World," that great table-land of Asia, extend- 

 ing northward from the Himalayas and their eastward 

 extensions to the Altai IMovmtains, &c. A detailed map 

 of this strange country is dotted over with figures, of tad- 

 pole shape, or of bags with strings attached. The strings 

 are rivers, the bags are salt lakes, most of them of briny 

 saltness. Many are surrounded with salt deserts, evi- 

 dently the beds of their ancient greater extension. I 

 suspect that during the great European glacial epoch, 

 when there was more vain and less evaporation, these 

 cul-de-sac lakes were united to form a great Asiatic 

 Mediterranean sea. The Sea of Aral and the Caspian 

 are larger examples of the same series. The saltness of 

 these is commonly supposed to indicate their former 

 communication with the ocean ; but their surroundings 

 contradict this, and what I have explained above removes 

 the demand for the geographical violence involved in the 

 supposition. Even if we assume that the Caspian was 

 formerly connected with the Black Sea, it was still beyond 

 the reach of ocean or even Mediterranean salt, as the 

 Black Sea pours outwards through the Bosphorus into 

 the Sea of Marmora, and this still outwards through the 

 Dardanelles, all downwards to the Mediterranean. 



Many analyses of sea-water have been made, the results 

 displaying notable variations, as I have already stated. 

 The following present an approximate average, as selected 

 by Dr. Miller :— 



British Channel. Mediterranean. 



In quoting these (the first is by Schweitzer, the second 

 by Usiglio), I should add that all such statements of 

 analytical results involve a certain amount of hypothesis. 

 The existence of the elements there named are demon- 

 .strated as fact, and also their quantities ; but the mode of 

 their grouping as compounds is merely inferred. Thus 

 some of the chlorine wliich is there given to the sodium, 

 the potassium, and the magnesium, may be actually 

 associated with the calcium, and a corresponding amount 

 of the sulphuric acid described as combined with the lime 

 may be actually associated with soda. The further dis- 

 cussion of this is not demanded here, and the subject is 

 still obscure ; but there is one remarkable and highly 

 instructive feature which exists independently of the 

 hypothetical assumptions. It is this : the materials most 

 abundant in the saline constituents <if sea-water are just 

 those earth materiah that are the most suluhle in distilled 

 water. 



Every student who has gone through his first practical 

 lessons in chemical analysis knows that, with one excep- 

 tion, he precipitates all the metals by causing them to 

 form insoluble compounds, this exception being sodium, 

 and that in ordniary course he finally estimates this as 

 soluble chloride, which he evaporates down to dry crystals. 

 This (our common table-salt) is the leading, the charac- 



teristic salt of sea-water. There is anolher base that 

 forms equally soluble salts to those of soda, viz. ammonia, 

 but this is not a constituent of the inorganic rock material 

 of the earth's crust, and therefore its comparative absence 

 rather favours the general view I am advocating. 



Still more elaborate analyses than thofe I have quoted 

 have been made, analyses conducted for the purpose of 

 discovering quantities too small to be detected by ordinary 

 means. Very large quantities of sea-water have been 

 evaporated down and the above-stated constituents 

 removed. By skilful application of this principle the 

 obscure, excessively dilutee! constituents have been con- 

 centrated and rendered evident. Thus have copper, silver, 

 gold, and many other metals been found in such quantities 

 as to suggest that, if we proceed far enough, we may find 

 all the materials of the earth dissolved in sea-water in 

 proportions bearing some relation to their solubility and 

 their abundance on the earth's solid surface. For example, 

 Sonnenstadt found -f'-^ of a gramme (about 14 grains troy) 

 of gold in every ton of sea-water. Otherwise stated, 

 eight tons of sea-water contain, within a small fraction, 

 the same quantity of pure gold as we have in an English 

 sovereign. Therefore, takmg the whole weight of the 

 ocean in tons and dividing by eight, we have the value of 

 the gold dissolved in the ocean expressed in pounds 

 sterling. 



The saltness of the sea has been attributed to the 

 solution of beds of rock-salt. This I believe to be just the 

 converse of the truth. The sea has not obtained its salt 

 fi-om such deposits, but such deposits have obtained their 

 salt from the sea or inland salt-lakes. The salt occurs 

 more or less admixed or interstratitied with marine or 

 lacustrine eleposits, indicating the existence of an ancient 

 sea or lake bottom from which the salt water has been 

 evaporated, forming first a salt-lake, then brine pools, 

 and finally the existing saline strata. 



I visteel the " Salines " or salt-mines of Bex m Switzer- 

 land many years ago, travelled a considerable distance 

 underground, expecting to see some of the glistening 

 crystal walls and grottoes of wliich I had read as displayecl 

 in salt-mines ; but, instead of these, found nothing but long 

 dark passages and galleries cut in dingy, grey, mud-like 

 rock. This is a characteristic example of such saline 

 deposits. They usually consist of dirty sulphate of lime 

 intermingled with grains of salt. The salt is obtained 

 therefrom by dissolving it out with water and then 

 evaporating the solution, ^^'hen the water reaches it by 

 natural infiltration salt-springs and salt-wells are formed, 

 and the supply is obtained by pumping from these. Such 

 is the case in Cheshire, Droitwich, itc. 



Now let us see what would occur if we were to fill a 

 tank with ordinary sea-water, and evaporate away the pure 

 water. The first observable result would be general tiir- 

 bielity. On examination we should find this turbidity to be 

 due to the gradual precipitation of sulphate of lime (plaster 

 of Paris), which, being the least soluble of all the salts 

 named in the above analyses (excepting the carbonate), 

 would be the first to come down in notable quantity. Next 

 to this, and simultaneously with its continuation, would 

 occur the deposition of crystalline grains of chloride of 

 sodium, the other salts following. If the water had been 

 taken from the deep sea and perfectly clear, the saline rock 

 thus formed would be white and glistening ; if from 

 estuarine shallow turbid water, it would be darker or more 

 or less dirty, like the rock matter at Bex. That it should 

 usually be thus dirty is only what is likely to occur under 

 the conelitions of silting up and shallowing that must 

 accompany the isolation and evaporating down of a body 

 of sea-water or salt-lake water. 



