NOVBMBER 16, 1900.] 



SCIENCE. 



751 



solid state by pressure, its volume is very 

 responsive to changes either of pressure or 

 temperature. The remarkable expansion 

 .of liquid carbon dioxide is a case in point : 

 120 volumes of this fluid at — 20° C. be- 

 comes 150 volumes at 33° C; a tempera- 

 ture just below the critical point. A great 

 change of volume also occurs when the 

 material of igneous rocks passes from the 

 crystalline stage to that of glass ; in the 

 case of diabase* the difference in volume 

 of the rock in the two states at ordinary 

 temperature is 13 per cent. If the relief 

 of pressure over the site of continents were 

 accompanied by volume changes at all ap- 

 proaching this, the additional elevation of 

 seventeen twenty-sevenths required to raise 

 the land to the sea-level would be accounted 

 for.f How far down beneath the surface 



* C. Barus so names the material on -which he ex- 

 perimented ; apparently the rook is a fresh dolorite 

 without olivine. 



t Professor Fitzgerald has been kind enough to ex- 

 press part of the preceding explanation in a more pre- 

 cise manner for me. He writes : " It would require 

 a very nice adjustment of temperatures and pressures 

 to work out in the simple way yon state it ; but what 

 is really involved is that in a certain state diabase 

 (and everything that changes state with a consider- 

 able change of volume) has an enormous isothermal 

 compressibility. Although this is very enormous in 

 the case of bodies which melt suddenly, like ice, it 

 would also involve very great compressibilities in the 

 case of bodies even which melted gradually, if they 

 did so at all quickly, i. e., within a small range of 

 temperature. What you postulate, then, is that at a 

 certain depth diabase is soft enough to be squeezed 

 from under the oceans, and that, being near its melt- 

 ing point, the small relief of pressure is accompanied 

 by an enormous increase in volume which helped to 

 raise the continents. Now that I have written the 

 thing out in my own way it seems very likely. It is, 

 anyway, a suggestion quite worthy of serious consid- 

 eration, and a process that in some places must al- 

 most certainly have been in operation, and may he is 

 still operative. Looking at it again, I hardly think 

 it is quite likely that there is or could be much 

 squeezing sideways of liquid or other viscous ma- 

 terial from under one place to another, because the 

 elastic yielding of the inside of the earth would be 

 much quicker than any flow of this kind. This 



the unloading of the continents would be 

 felt it is difiBcult to say, though the problem 

 is probably not beyond the reach of mathe- 

 matical analysis ; if it afifected an outer en- 

 velope twenty-five miles in thickness, a lin- 

 ear expansion of four per cent, would sufi&ce 

 to explain the origin of ocean basins. If 

 now we refer to the dilatation determined 

 by Carl Barus for rise in temperature in the 

 case of diabase, we find that between 1093° 

 and 1112° C. the increase in volume is 3.3 

 per cent. As a further factor in deepening 

 the ocean basins may be included the com- 

 pressive effect of the increase in load over 

 the ocean floor ; this increase is equal to 

 the pressure of a column of water 0.675 

 mile in height, and its effect in raising the 

 fusion point would be 2° C, from which we 

 may gain some kind of idea of the amount 

 of compression it might produce on the 

 yielding interior of the crust. To admit 

 that these views are speculative will be to 

 confess nothing ; but they certainly account 

 for a good deal. They not only give us 

 ocean basins, but basins of the kind we 

 want, that is, to use a crude comparison 

 once made by the late Dr. Carpenter, ba- 

 sins of a tea-tray form, having a somewhat 

 flat floor and steeply sloping sides ; they 

 also help to explain how it is that the value 

 of gravity is greater over the ocean than 

 over the land. 



The ocean when first formed would con- 

 sist of highly heated water, and this, as is 

 well known, is an energetic chemical re- 

 agent when brought into contact with sili- 



would only modify your theory, because the diabase 

 that expands so much on the relief of pressure might 

 be that already under the land, and raising up this 

 latter, partly by being pushed up itself by the elastic 

 relief of the inside of the earth and partly by its own 

 enormous expansibility near its melting point. The 

 action would be quite slow, because it would cool it- 

 self so much by its expansion that it would have to 

 be warmed up from below, or by tidal earth-squeez- 

 ing, or by chemical action, before it could expand 

 isothermally. 



