Dec, 5, 18S9] 



NA TURE 



10 



denser is placed in a vacuum, then, so far as I can see. Prof. 

 Lodge's principle must lead to th^ conclusion that the difference 

 ■of potential between the plates of the conden-^er is proportional 

 to the Peltier effect ; but if this is so, it is quite easy to show by 

 the second law of thermodynamics that if the system i? regarded 

 as a heat-engine, the Peltier effect cannot vanish except at the 

 zero of absolute temperature. 



On the other points mentioned by Prof, Lodge in his letter, 

 there does not seem sufficient difference of opinion between us 

 to make it worth while discussing them. 



In conclusion, let me assure Prof. Lodge that I am thoroughly 

 in sympathy with the view that the consideration of the be- 

 haviour of the medium in the electric field is absolutely 

 •essential. I do not think there is anything inconsistent with 

 this in the paragraph he quotes, which was intended to express 

 what is well known to have been the opinion of Maxwell him- 

 self — that the key to the secret of electricity would be found in 

 the "vacuum" tube. The Reviewer. 



The Physics of the Sub-oceanic Crust. 



In your article on the above subject in Nature of 

 ■November 21 (p. 54^ the important proposition that the 

 -earth's crust rests on a liquid layer is once more brought to the 

 front. The question reaches to the very basis of geology, but, 

 like most of those of real importance, is not now recognized 

 by the Society which occupies apartments in Burlington House, 

 rent free, for the purpose of forwarding the study of geology. 



Nothing is more obvious to the geological student than that 

 enormous thicknesses of strata have been formed at practically 

 ■one level. We do not find that, when a thousand feet of sedi- 

 ment has been deposited under water, the deposition began in 

 ■water which was 1000 feet deep, and went on gradually lessen- 

 ing the depth until the sea or lake was filled up ; but we do find, 

 as in the coal-measures, that the entire 1000 feet was deposited 

 in most uniformly shallow water ; that therefore the crust of the 

 earth must have sagged foot by foot as additional feet of burdens 

 were laid upon it. Deltas that have not yet been bottomed show 

 hundreds of feet of silt, every yard of which was deposited at 

 only a few feet from the surface level of the water ; eUuaries and 

 river valleys slowly sink where there is sedimentation ; ice-caps tell 

 ■of accumulation ace 'mpanied by depression and submergence, 

 and re-elevation when the burden is melted and dissipated ; 

 ■coral formations and submergence are regarded as well-nigh 

 inseparable, and even lava-flows flowing on to a plain have 

 sunk its level in a degree corresponding with their mass. 

 Where there is fifty or a thousand feet of piled-up lava-sheets you 

 may look for a fault of like amount on its flanks, like that which, 

 still unsuspected by geologists, cuts the Isle of Mull in half. 

 Whether we look at the past or the present, we seem to see 

 evidence of a crust resting in equilibrium on a liquid layer, and 

 sensitive to even apparently insignificant readjustments of its 

 weight. And if the crust did not respond to, and make room 

 for, the burdens laid upon it by the removal of disintegrated 

 land and its redeposition as silt under water, would not the seas 

 be choked for miles round every coast ? The abrading action of 

 the waves cuts down the land, be it high or low, to a dead 

 uniform level, and sooner or later it must become first beach, 

 and then sea-bottom. There it is covered with silt or sea-weed, 

 and is no longer abraded, and would, therefore, form great level 

 tracts, instead of almost uniformly shelving coasts, unless it 

 yielded pari passu to the increasing weight of sedinient and 

 water. The immediate effect of cutting down cliffs, say of 100 

 feet in height, and removing them in solution or by wave action, 

 is to relieve the pressure at their base ; and I claim that, wherever 

 I have excavated for the purposes of collecting under such 

 conditions, I have found a decided slope inwards away from the 

 sea, if the strata were at all horizontal, no matter what direction 

 their general inclination might be at a distance from the sea 

 margin. But on the beach, a little way from the base of the 

 •cliffs, the slope is, on the contrary, towards the sea, and whatever 

 ■the general inclination may be, we see the harder ledges, even 

 if but a few inches thick, sloping away into deeper and deeper 

 water until lost to view ; and if you choose to follow them and 

 dredge, you trace them tending downwards into yet deeper 

 water. This appears to me to be simply because the relief fr)m 

 pressure has made the beach-line the crown of a slight arch, and 

 an arch that continues to grow and travel, else how could we 

 collect day after day and year after year, on the same spots, such 

 as Eastware or Bracklesham Bays, fresh crops of fossils after 



every tide? I have hundreds of times picked up every vestige 

 of a fossil on perhaps an acre of Eocene or Gault, yet a couple of 

 tides have removed so appreciable a layer that the area has 

 appeared studded with fresh specimens that were twenty-four 

 hours previously wholly covered and concealed under matrix. 

 Yet this ceaseless waste does not lower the level of the beach as 

 it ought to. 



And if such slight displacements as result from coast denuda- 

 tion have so appreciable an effect, what must take place in 

 ocean, if subsidence is going on, and the weight of water on the 

 increase ? Darwin saw th.at the vast rise of land, which he so 

 graphically describes in South America, must have been accom- 

 panied by a corresponding depression in the bordering oceans ; 

 and in turning his pages you almost expect to come on the view 

 that depression in the Pacific must be the cause of the upheaval 

 of the coastline. It only wanted the liquid layer theory to 

 make the dependence of one on the other obvious. No general 

 rise of land has, or ever can, take place, under the overwhelm- 

 ing pressure of the great ocean depths, and oceans are thus 

 permanent ; the struggle is confined to whether the liquid layer 

 shall overcome lateral resistance and find relief along the coast- 

 lines, which are the nearest lines of least resistance, and already 

 weakened by abrasion, forming coast ranges, or rending the 

 crust, and pouring over thousands of square miles from fissure 

 eruptions ; or whether it shall overcome vertical resistance, and 

 raise the beds of shallower ocean eventually, perhaps, into land. 



Thus the tendency, as noticed by the writer of your article, is 

 for deep oceans to become deeper, under pressure which may 

 increase but never relaxes, and for mountain-chains to grow into 

 higher peaks, the more weight is lessened by valleys being cut 

 up and denuded. 



This theory accounts for innumerable facts in the physics of 

 the earth which space would not permit me to enter on, and is, 

 so far as I know, opposed to none. 



J. Starkie Gardner. 



Area of the Land and Depths of the Oceans in 

 Former Periods. 



In a letter to Nature (p. 54), entitled " Physics of the Sub- 

 oceanic Crust," by my friend, Mr. Jukes-Browne, the following 

 passage occurs : — 



" We are at liberty to imagine a time when there was much 

 more land than there is at present, and when all the oceans were 

 comparatively shallow." 



I wish to point out that such a condition of things could not 

 obtain if the bulk of the ocean water was the same as now. To 

 get more land, the ocean would have to be deeper than now, not 

 shallower. An easy way of conceiving the effect of shallowing 

 the oceans is to mentally lift up the present ocean-floors, the 

 result being an overflow of water and decrease of land area. 

 The only possible way of shallowing the oceans and increasing 

 the area of the land W(iuld be to make the ocean-floors perfectly 

 flat, and to surround the continents with vertical walls of rock 

 — in fact, to make the oceans into docks, which nevertheless 

 would exceed two miles in depth. 



I pointed out this geometrical fact in " Oceans and Con- 

 tinents " ^ — an article which has provided some of the stock 

 arguments against their fixity. If, therefore, theorists feel it 

 necessary that the land areas should be greater, and the oceans 

 shallower, in former ages, they are bound at the same time to 

 provide some means of decreasing the bulk of the ocean waters. 

 This seems difficult, as other theorists tell us that the amount of 

 water on the globe goes on decreasing, being used up in the 

 hydration of the crust of the earth, and point to the condition of 

 things on the moon as the final stage of our planetary existence. 



T. Mellard Reade. 



Park Corner, Blundellsands, near Liverpool, 

 November 23. 



Distribution of Animals and Plants by Ocean Currents. 



Sous ce titre, vous donniez nagucre (vol. xxxviii. p. 245) 

 une correspondance de M. A. , W. Buckland concernant divers 

 phenomenes observes k Port-Elisabeth, dans I'Afrique du Sud. 

 Entre autres choses il y etait relate que, vers la fin de I'ann^e 

 1886, un fruit analogue a.celui du cocotier avail ete porte par la 

 mersur le rivage de Port- Elisabeth en meme temps que des quan- 

 tites considerables de pumites ou pierres-ponces. 



' Geo'o^kal Magazine. 1880, p. 389 ; also, see letter in same magazine, 

 i38i, p. 335, headed " subsidence and Elevation." 



