296 EVOLUTIONAL GEOLOGY. 



pressure its volume is very responsive to chanoe.s, either of pressure 

 or temperature. The remarkable expansion of liquid carbon dioxide 

 i.s a case in point: 120 volumes of this fluid at —20^ C. become 150 

 volumes at 33° C, a temperature just below the critical point. A great 

 change of volume also occurs when the material of igneous rocks 

 passes from the crystalline state to that of glass. In the case of dia- 

 l)ase^ the ditierence in volume of the rock in the two states at ordinar}- 

 temperatures is 13 per cent. If the relief of pressure over the site of 

 continents were accompanied ])y volume changes at all approaching 

 this, the additional elevation of seventeen twenty-sevenths required to 

 raise the land to the sea level would be accounted for.' How far down 

 beneath the surface the unloading of the continents would be felt it is 

 difficult to say, though the problem is probably not beyond the reach 

 of mathematical analysis; if it aftected an outer envelope^ 25 miles in 

 thickness, a linear expansion of 4 per cent would suflice to explain the 

 origin of ocean basins. If now we refer to the dilatation determined 

 by C'ai'l Barus for rise in temperature in the case of diabase, we And 

 that between 1,01^3' and 1,112- C. the increase in volume is 3.3 per 

 cent. As a further factor in deepening the ocean basins may be 

 included the compressive effect of the increase in load over the ocean 

 floor; this increase is equal to the pressure of a column of water 0.(375 

 mile in height, and its eflect in raising the fusion point would ])e 2 



^ C. Barus so names the material on which he experimented. Apparently the rock 

 is a freyh dolerite without olivine. 



■^Professor Fitzgerald has lieen kind enough to express part <if the preceding 

 explanation in a more precise manner forme. He writes: "It would require a very 

 nice adjustment of temperatures and pressures to work out in the simple way you 

 state it, but w^hat is really involved is that in a certain state diabase (and everything 

 that changes state with a considerable change of volume) has an enormous isother- 

 mal compressil)iiity. Although this is very enormous in the case of bodies which 

 meft 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, ])eing near 

 its melting 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 consideration, and a process that in some places must almost certainly 

 have been in operation and maybe is still operative. Looking at it again, I hardly 

 thmk it is quite likely that there is or could be much squeezing sideways of liquid or 

 other viscous material from under one place to another, because the elastic yielding 

 of the inside of the earth would be nuich quicker than any flow of this kind. This 

 would only modify your theory, because the diabase that expands so nmch on the 

 relief of pressure might be that already imder 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 itself so much by its expansion that it would 

 have to be warmed up from below or by tidal earth squeezing or by chemical action 

 before it could expand isothermally." 



