Mr, 0. Fisher — Changes of Latitude on the Earth'' s Surface. 295 



It cools and hardens so rapidly on exposure, that it may be walked 

 upon within a few hours after coagulating. Sometimes upwards 

 of fifty small cones and craters, more or less in activity, have been 

 counted on the floor of this great pit. They were from fifty to 

 a hundred feet high."^ "It is nine miles in circumference, and its 

 lower area, which not long ago fell about 300 feet, just as ice on 

 a pond falls when the water below it is withdrawn, covers six 

 square miles." ^ In the case of the earth's crust, it seems probable 

 that the lateral pressure, to which the upheavals and subsidences 

 are due, would have the effect of keeping the fragments of the crust 

 close pressed together, and so checking anything like a general 

 intrusion of lava between them. Its exit would probably be con- 

 fined to here and there volcanic vents, more numerous, no doubt, 

 and larger, in ancient times, but still in general character like those 

 of the present day. 



The argument for the existence of a fluid layer beneath the 

 present crust appears to me to be considerably strengthened by 

 a comparison which I have myself made between the actual in- 

 equalities of the earth's surface and those which could have been 

 formed by lateral pressure if the globe had cooled as a solid body.^ 

 This has led me to the conclusion that some condition has been 

 present which has admitted of its shrinking much more than it 

 could have done if it had cooled as a solid ; nay, probably more 

 than mere cooling alone can account for. I surmise therefore that 

 the interior has contained water, which has escaped through volcanic 

 vents as superheated steam, and that the earth's volume has been 

 diminished in that manner by the actual transference of matter 

 from beneath to above the crust. What may be the exact amount 

 of decrease of volume which might be obtained by transferring 

 a given quantity of water from beneath to above the crust, it is not 

 possible to say ; because we do not know the properties of water 

 as it may exist under such circumstances of heat, pressure, and 

 chemical combination as obtain within the earth. But it is obvious 

 that a larger contraction can be accounted for by aid of this supposi- 

 tion than without it. I received a letter from Mr. Scrope in October, 

 1876, very shortly before his death, in which he commented on this 

 suggestion. "There is one of the points you put forward which never 

 struck me before, but which now appears to me most valuable ; 

 viz., that the enormous amount of steam that has escaped from the 

 interior in early times, as well as down to the present, has been, and 

 is, the cause of those suhsidences of the crust, to which the basins of 

 seas and oceans, and the crumplings of the terrestrial rocks are owing, 

 far more than to any general contraction of the nucleus by cooling." 



It is known also that mountain chains have most of them been 

 ridged up and folded much more than the country bordering upon 

 them. Now this peculiarity implies a slip of the superficial strata 



1 Scrope's Volcanos, p. 477, ed, 1862. 



' Miss Birt's Hawaiian Archipelago. See Nature, vol. xi. p. 324. 

 ^ Trans. Cambridge Phil. Soc, vol. xii. part ii., abstracted in Geol. Mag. N.S. 

 Vol. I. p. 60. 



