484 SCIENCES OF THE EARTH 



process pursues a long course and at the end conclusions of great 

 import are often drawn. Usually the process rests there, and in this 

 lies a serious shortcoming. It should give rise to a new process of 

 a higher order. Not seldom, a critical study of the results will reveal 

 features that were not recognized nor suspected in the original 

 assumptions, though really there. Out of these revelations should 

 grow new assumptions and a new process. The second conclusion 

 may in like manner betray unsuspected qualities, and these should 

 beget still other assumptions, and so the procedure should continue 

 until the field is exhausted. 



To choose a specific illustration is not a little delicate, for to be 

 most familiar it must be of the negative type, but I fear such an 

 illustration is the only way to convey clearly the meaning here in- 

 tended. I therefore venture to choose one so eminent and so admir- 

 able, even with its limitations, that any suggestion of shortcoming 

 will in no wise dim the luster of a great achievement. In the classic 

 investigations of George Darwin on tides and their astronomic 

 consequences, a viscous earth is assumed as the starting-point, with 

 properties such that the tidal protuberance is carried forward by 

 the rotation of the earth to the point which gives the maximum 

 effect on the motions of the earth and moon. These assumptions 

 run potentially through the whole train of brilliant mathematical 

 deduction. At the end of the inquiry, or if not of this particular 

 inquiry, at least of collateral inquiries, the conclusion is reached 

 that the earth is a rigid body comparable to steel. Between such a 

 rigid body and such a viscous earth as was assumed at the outset of 

 the inquiry, there is a seeming incongruity. This, under the regen- 

 erative method, suggests a new investigation on the assumption 

 that the earth is a very rigid body, with the further assumption that 

 it has high elasticity of form, such that its protuberance may perhaps 

 not be carried forward to the degree previously postulated. These 

 new assumptions are the more imperative because they are sup- 

 ported by inquiries based on quite independent lines. In framing 

 the new hypothesis an advance in detail and in organization is to be 

 sought on the evolutionary principle already indicated. If the earth 

 as a whole is as rigid as steel, and the outer part is, as we know, 

 formed of rock much less rigid than steel, the interior must be much 

 more rigid than steel, and there must be a differential distribution of 

 rigidity. The new inquiry may then well start with the assumption 

 of increasing rigidity toward the centre. Postulating an earth so 

 constituted, a first step of the regenerated inquiry might well be an 

 effort to learn not only the amount of the tidal protuberance, but 

 also the position of the protuberance, since its position is as essential 

 as its amount in influencing the motions of the earth and moon. As 

 a geologist I venture to entertain the belief that exhaustive inquiry 



