716 REPORT— 1900. 



states at ordinary temperatures is 13 per cent. If tlie relief of pressure over the 

 site of continents were accompanied by 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 is difficult to say, though the problem 

 is probably not beyond the reach of mathematical analysis; if it affected an outer 

 envelope twenty-five miles in thickness, a linear expansion of R per cent, would 

 suffice 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 compressive 

 effect of the increase in load over the ocean floor : this increase is equal to the 

 pressure of a column of water 0-(i75 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, basins 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 consist of highly heated water, and this, 

 as is well known, is an energetic chemical reagent when brought into contact 

 with silicates like those which formed the primitive crust. As a result of its action 

 saline solutions and chemical deposits would be formed ; the latter, however, 

 would probably be of no great thickness, for the time occupied by the ocean in 

 cooling to a temperature not far removed from the present would probably be 

 included within a few hundreds of years. 



The Stratified Series. 



The course of events now becomes somewhat obscure, but sooner or later the 

 familiar processes of denudation and the deposition started into activity, and have 

 continued acting uninterruptedly ever since. The total maximum thickness of 



' Professor Fitzgerald has been kind enough to express part of the preceding 

 explanation in a more precise manner for me. He writes : ' It would require a very 

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

 state it ; but what is really involved is that in a certain state diabase (and everything 

 that changes state with a considerable 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 

 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 think 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 much quicker than any flow of 

 this kind. This 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 itself so much by its expansion 

 that it vjould have to be warmed up from below, or by tidal earth-squeezing, or by 

 chemical action before it could expand isotheripally,' 



