228 



OBJECT OF THE SALT CONDITION OF THE SEA. 



[1865. 



ting power of the inarine Mollu.sks and Radiata,* in withdraw- 

 ing from the sea the various salts brought into it by rivers, no 

 one appeal's to have hinted, even, at the further eii'ects due to 

 this action. 



But these organic agencies are mainly referrible to the ab- 

 straction of the lime salts from the sea water ; the object of 

 the chloride of sodium — the principal saline constituent of the 

 pressure of the sea — ^being sought to be explained by the first 

 hypothesis •,'f and it is here that I venture to differ from you, 

 and to prefer my own explanation, as published in the March 

 number of the Canadian Journal. 



The surface water of the sea would necessarily be rendered 

 Salter, and consequently heavier, than the underlying strata, 

 were no antagonistic influences at work; but I think we have 

 sufficient experimental evidence to show that the effects of eva- 

 poration are counteracted by the constant additions of fresh 

 water which the ocean receives at its surface, and by the com- 

 par-atively high temperature of this latter (the surface) in those 

 regions where evaporation is the most active. Comte d' Archiac, 

 in his compendium of the Physics of the Globe (Vol. 1 of his 

 Histoire des Progres de la Geologic) has the following observ- 

 ations : — " Les recherches faites sur la composition des eaux 

 recueillies en mer pendant le voyage de la corvette La Bonite, 

 ont deuiontr(5 que dans I'Ocean Atlantique, le Golfe du Ben- 

 gale, rOcean Indicn, et I'Ocean Atlantique Meridonale, la 

 densite genorale de I'eau prise a la surflice etait moindre que 

 celle de I'eau prise a une certaine profondeur. Une seule ex- 

 ception a eette regie a ete reconnue. A une seule exception 

 pres aussi, le degre de salure est plus prononce au fond [I sup- 

 pose he means at considerable depths, not absolutely at the 

 bottom] qu' ii la surface. "| This view is in accordance, I be- 

 lieve, with the usually received opinion. § Prom all that I have 



* And we may add that of marine vegetation also. Dr. Lyon Play- 

 fair was, I believe, the first to suggest the action of Algoe in abstract- 

 ing carbonic acid from the water, and thus setting free the carbonate 

 of lime.— E. C. 



f " The vapor is taken from the surface water ; the surfece water 

 thereby becomes more salt, and consequently heavier ; it tlierefore 

 sinks ; and hence we have due to the salts of the sea, a vertical circu- 

 lation, viz., a descent of heavier — because Salter and cooler — water 

 from the surface, and an ascent of water that is lighter — because it is 

 not so salt — from the depths below." — Lieut. JIaury ; Wind and Cur- 

 rent Charts, 6th ed. p. 182. This view has been entertained, however, 

 by other observers. Thus, Sir Charles Lyell, in liis " Principles of 

 Geology," has the following remarks in reference to the Mediterranean 

 — ■'■ After evaporation, the surface water becomes impregnated with a 

 slight excess of salt, and, its specific gravity being thus increased, it 

 instantly falls to the bottom, while lighter water rises to the top, &c." 

 But here we have to consider, how far this surface water could sink 

 without yielding a portion of its extra salt to the surrounding water, 

 and so rendering the whole uniform. I question altogether the proba- 

 bility of a vertical descent of this kind taking place in ordinary seas, 

 at least to any depth. Over broad areas, moreover, it would neces- 

 sarily be subject to frequent and often long-continued interruptions. — 

 E.G. 



J " The results of the chemical examination of samples of sea-water 

 collected during the voyage of the corvette La Bonite, have shown, 

 that, in the Pacific Ocean, the Gulf of Bengal, the Indian Ocean, and 

 the South Atlantic, the general density of water taken from the surface 

 was less than that taken from a certain depth. Only a single excep- 

 tion to this law was noticed. With little more than a single exception, 

 also, the degree of saltness was greater at great depths than at the 

 surface." See also comp. rend., yol. vi., p. 616, from which the above 

 is quoted. — E. C. 



?. Theoretically, the surface water, owing to evaporation,, should be 

 slightly cooler than the stratum of water immediately below it. I 

 allude, of course, to warm and temperate seas.^E. C: 



read and thought upon the subject, it appears to me that in the 

 phenomenon of the, so to say, reversed inequalities of tempera- 

 ture between the surface and deep water in the intertropical 

 and polar regions, we have the main cause of oceanic move- 

 ments. With all this, however, I do not mean to infer that 

 the principle announced by you is to be wholly disregarded, in 

 our attempts to frame a satisfactory hypothesis respecting the 

 object of the saltness of the sea. In stiivingto uphold my own 

 theory, I have done so, perhaps, in too exclusive a spirit. 



With regard to the origin of the saline components of sea- 

 water, you adopt, I perceive, the views of tlie elder Darwin and 

 others, to the effect that these components have been entirely 

 despoiled from the land, by springs and rivers, and so carried 

 into the deep, the action continually going on. But here, 

 again, you must allow me to differ from yoii. My reasons for 

 this dissent are the following,^ — First, the striking preponder- 

 ance of chloride of sodium over the other salts in sea-water ; 

 whereas, amongst the saline matters generally present in river- 

 water,it by no means occupies a very conspicuous place. But even 

 if the sea were fed by brine springs instead of rivers, my argu- 

 ment would still hold good; for in nine cases certainly out of 

 every ten, these brine springs would be but returning to the 

 ocean, what, in former geological epochs, the ocean had ren- 

 dered to the land. Fownes's assertion, quoted in your note at 

 page 179,* appears to me to be altogether untenable, or at least 

 without true bearings on the point at issue. Lakes, so pecu- 

 liarly conditioned as these of which he speaks, have evidently 

 not been rendered salt (in the common acceptation of the teim) 

 by the rivers which flow into them, but have been salt from the 

 beginning — as portions of ancient seas cut off' from the main 

 ocean by geological changes. Secondly, according to this view, 

 the sea at one time must have been far less salt than at pre- 

 sent, and have gradually become Salter and Salter — an infer- 

 ence, ' the assumption of which is scarcely warranted on 

 palseontological data.f 



This objection might be met, however, by assuming that marine 

 life was created, as a compensating agent, so soon as the sea 

 attained to its present saltness, and not before. I place, there- 

 fore, no great stress upon it. 



Finally, may we not legitimately seek to ascertain why chloride 



* "The case of the se.a," says Fownes, "is what occurs in every 

 lake into which rivers flow, but from which there is no outlet except 

 by evaporation. Such a lake is invariably a salt lake. It is impos- 

 sible that it can be otherwise ; and it is curious to observe that this 

 condition disappears when an artificial outlet is produced for the wa- 

 ters." — Lieut. Maury. To this I replj', that, owing to the compara- 

 tively small amount of chloride of sodium in ordinary river waters, a 

 lake of this kind, if originally fresh, would become silted up by depo- 

 sition of carbon.ate of lime, &c., long before it could possibly exhibit 

 the composition of the ocean. An originally salt hake would necessarily 

 become fresh in course of time, if river waters were constantly poured 

 into it, and an outlet also provided by lower levels to the sea. If we 

 place at three diflFerent levels, an empty vessel, a vessel containing a 

 salt solution, and one filled with ordinary water, this latter occupying 

 the highest level, and connect the three by strips of filtering paper, 

 or a few cotton threads to act as syphons, the contents of the middle 

 vessel (here representing the salt lake) will be gradually replaced by 

 the water from above, and transferred to the under vessel. AVhere no 

 outlet is provided, local conditions, on the other hand, as in the case of 

 the Dead Sea, may modify to a marked extent the original composition 

 of the water. — E. C. 



f I am quite aware that the study of Fossil Ichthyology offers some 

 slight support to theview mentioned in the text ; but this, at the best 

 of doubtful acceptation, is completely outbalanced, on the ot er liond, 

 if we take into consideration the immense numbers of radiated ani- 

 mals, brachiopods,cephalopods,and other types which preceded fish-life, 

 and which were undoubtedly marine. — E. Ci 



