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NATURE 



[Dec. 12, 1889 



T am so strongly tempted unreservedly to accept the " pro- 

 tective " theory, that I perhaps lay too great stress on these 

 negative instances. As a matter of fact, I suppose that the 

 experience of a single individual is rarely large enough to justify 

 any induction being made from it. I myself, for instance, have 

 never come across the extreme variations of the cuckoo's egg, 

 such as Seebohm figures. E. B. TiTCHENER. 



3 Museum Terrace, Oxford, December 3. 



Is the Bulk of Ocean Water a Fixed Quantity ? 



Mr. Mellard Reade's criticism is perfectly sound. If the 

 bulk of the ocean water on the surface of the globe has always 

 been the same, the oceans could not at any time have been 

 shallower than at present without a decrease in the area of the 

 land. Consequently, the supposition that in early geological 

 times the area of the land was larger, and the depth of the 

 oceans less, demands the further inference that the bulk of the 

 ocean water was less then than it is now. 



When writing on the physics of the sub-oceanic crust, I saw 

 that this was a necessary consequence of the theory, but I was 

 not then quite prepared to discuss it. I have since had some 

 correspondence with Prof. A. H. Green and Mr. O. Fisher on 

 the subject, and will briefly indicate the possibilities that have 

 occurred to u^. 



The first suggestion made was that, if the solar radiation was 

 greater in Palaeozoic times, there would be greater evaporation, 

 and as the temperature of the air would also be higher, the 

 atmosphere could hold more aqueous vapour than it does now, 

 so that we might suppose a part of the water which is now in 

 the ocean to have been then permanently suspended above it. 

 Mr. Fisher, in writing to me, admits this possibility, and even 

 thinks it might be feasible to estimately roughly the amount of 

 water so suspended if the mean temperature of the ocean at any 

 period was known. But he says : — " I dj not think you could 

 get much diminution of the oceans in this way, for, suppose the 

 present atmosphere to consist of nothing but aqueous vapour, 

 then it would represent a layer of water about 30 feet thick 

 evaporated from the earth's surface. Now, it seems hardly 

 probable that at a former time there should have been an amount 

 of aqueous vapour in the atmosphere so great that the mass of 

 suc'i additional vapour should equal that of all the oxygen and 

 nitrogen and vapour now in the atmosphere ; and even if there 

 was this amount, it would take off only about 30 feet of water 

 from the surface of the globe," or about 37 feet from the present 

 surface of the oceans. 



If, therefore, the bulk of the wa'er on and above the surface 

 of the earth has remained the same since the time when the 

 ciust was first formed, it seems difficult to find any means of 

 sensibly diminishing the amount of water in the oceans. But 

 need we make this preliminary assumption, and is it not really 

 possible that there has been an increase in the bulk of surface- 

 water, and not a decrease by absorption, as some theorists would 

 have us think ? May we not suppose, in fact, that water-sub- 

 stance has always existed in the interior of the earth, and may 

 it not, by its constant and gradual escape, have always been 

 adding to the bulk of the surface-waters ? 



This idea had occurred to Mr. Fisher so long ago as 1873, and 

 the following passage occurs a paper then published (Trans. 

 Camb Phil. Soc, vol. xii., Part 2, p. 431) : " If such was the 

 condition of the interior in the early stages of the cosmogony, 

 a large portion of the oceans now above the crust may once have 

 been beneath it " ; and in the new edition of his "Physics of 

 the Earth's Crust " he further discusses the manner in which 

 this water-substance may be diffused through the magma of the 

 liquid substratum beneath the crust. 



As a matter of fact, it is well known that almost all volcanoes, 

 when in eruption, emit large quantities of steam, and the pre- 

 sence of this steam has always been connected with the causes 

 of volcanic activity. There are only two ways of accounting 

 for the presence of this steam : (i) that water from the sea or 

 from the rainfall gains access to the deep seated foci of volcanic 

 action ; (2) that the water-substance is a primary constituent of 

 the liquid magma below, and that when this material is forced 

 up to the surface, the pressure which kept the water in solution 

 or combination is removed, and it is blown off as steam. 



As regards the first possibility, there are great difficulties in 



the way of supposing that surface-water can find its way to 



any region where the heat is sufficient to keep rock constantly 



»in a liquid condition. It does seem possible that the access 



of water to the interior parts of a volcano already established 

 may sometimes cause an eruption, and, under certain circum- 

 stances, an eruption of great violence ; but the descent of 

 water through the earth's crust to depths of 20 or 30 miles so as 

 to be the initial cause of the establishment of volcanoes is not so 

 easy to understand. The pressure of the superincumbent rocks 

 at a depth of 2 or 3 miles must be so great that all cracks and 

 interstitial spaces would be reduced to a minimum, and at the 

 depth of 5 miles one would suppose that none such could exist. 

 Several facts are known to geologists which show that all cracks 

 diminish rapidly downwards. One such fact is that in many 

 deep mines the throw of a. fault diminishes with the depth to 

 which it is followed. Another is the existence of such warm 

 springs as those of Bath, the explanation of which is supposed 

 to be that water percolating downward (say from the Mendips) 

 reaches a depth at which there is less resistance to its travelling 

 laterally than to its further descent, and that ultimately reaching 

 a crack or fault, it is forced up this path of least resistance by 

 the hydrostatic pressure of the descending stream. 



It is true that a residuum of the water might continue its down- 

 ward journey, being, as it were, slowly sucked downward as far 

 as the minutest interstitial spaces extended ; but what would 

 happen when it reached the lower layers of the crust ? Could it 

 possibly reach and be absorbed by or dissolved in the semi-fused 

 rock which must there exist? Captain C. E. Button has well 

 expressed this difficulty. Referring to the high temperature which 

 must exist at a depth of 5 or 6 miles, he says: — "At such a 

 temperature the siliceous materials of which the rocks are com- 

 posed are no lon;?er hard 'and brittle as when they are cold, but 

 viscous and plastic. . . . Now a crack or fiisure might reach 

 very far down into hard, cold, brittle rocks, but into soft semi- 

 fused plastic rocks, never. Under a pressure of several miles of 

 superincumbent strata, a crack, or even the minutest vesicle, 

 would be tightly closed up as if its walls were wax or butter. A 

 more perfect packing against ingress of water could not be con- 

 ceived." ^ 



Even capillary action could not come into play un-^er such 

 conditions as these. 



Let us next consider the alternative theory suggested by Mr. 

 Fisher. He claims that geologists furnish him with a certain 

 amount of positive evidence for the idea that water is an essential 

 constituent of the liquid magma from which the igneous rocks 

 have been derived. Passing over the proofs of the existence of 

 water in the crystals of volcanic rocks and in the materials of 

 deep-seated dykes, let us come at once to granite, a rock which 

 can only have been formed at great depths and under great 

 pressures, and which often forms large tract ■; that are supposed 

 to have been subterranean lakes or cisterns of liquid matter in 

 direct communication with still deeper reservoirs. Now, all 

 granites contain crystals of quartz, and these crystals include 

 numerous minute cavities which contain water and other liquids ; 

 and the quartz of some granites is so full of water-vesicles that 

 Mr. Clifton Ward has said : "A thousand millions might easily 

 be contained within a cubic inch of quartz, and sometimes the 

 contained water must make up at least 5 per cent, of the whole 

 volume of the containing quartz." This amount only represents 

 the water that has been, as it were, accidentally shut up in the 

 granite, for some was doubtless given off in the form of steam 

 which made its way through the surrounding rocks. 



It is therefore generally conceded that granite has consolidated 

 from a state of igneo-aqueous fusion, and that the liquid magma 

 from which all granitic intrusions have proceeded contains water- 

 substance. It is therefore only a step further to assume that this 

 water-substance is an essential constituent of the liquid sub- 

 stratum, and to suppose that it has been there since the con- 

 solidation of the earth. That there is no inherent improbability 

 in this supposition, and that it is not inconsistent with chemical 

 views of cosmogony, Mr. Fisher has shown at the end of his 

 chapter on the " Liquid Substratum." 



I am only now concerned with it as an explanation of the 

 secular increase in the bulk of the ocean waters which is 

 demanded by my theory of the evolution of continents and 

 oceans. We can prove from the geological records that volcanic 

 action has always been in operation from the very earliest times 

 in the world's history, and if it is true that such a reservoir of 

 water-substance has always existed in the earth's interior, the 

 continual volcanic eruptions must have constantly added water 

 to the oceans on the earth's surface. Hence, as I stated in my 



' " Volcanoes," by C. E. Dutton, in Ordnance Notes, No. 343, Washing- 

 ton, 1889. 



