318 A. Vaughan — Critique on Results of a Shrinldng Globe 



rests. Hence it follows that an absolute vacuity must be formed 

 under the fold, since in no way could a shell of expanding material 

 exert a squeezing force on the rocks beneath. Thus the undermost 

 of the layers which constitute the fold must support the whole weight 

 of the overlying mass. This result does not seem to accord well 

 with the potent effects which are attributed to the weight of over- 

 lying rocks in the direction of causing, what Mr. Eeade calls, 

 compressive extension. But, in fact, 1 believe that there is an 

 element of unreality which renders the whole conception invalid. 

 In the first place, so far as the effect of heat upon the actual 

 sediment is concerned, this sediment is deposited, not as solid rock, 

 every component particle of which is in closest union with its 

 fellows, but rather as a great number of small particles, each of 

 which has, so to speak, plenty of elbow room. It would seem then 

 that the effects of increase in pressure and temperature would be 

 mostly used up in welding the rock into a dense mass; each particle 

 expanding into the interspaces surrounding it, and the greater the 

 resistance to general expansion the more closely would each particle 

 be forced into union with its neighbours. This, surely, is in agree- 

 ment with the actual facts observed in the lowest of a great series 

 of conformable sedimentary strata. But, as regards the actual floor 

 and the rocks which lie beneath it, which may be supposed to be in 

 a dense state and not to admit of any great expansion of separate 

 particles, I believe that the effect of expansion will only tend to 

 minimize the contraction which, I now attempt to show, must be 

 in progress. 



It will, assuredly, be readily granted that, to allow of the 

 accumulation of the great thickness of sediment here conceived, 

 there must be an approximately proportional depression of the floor, 

 and such depression must imply the curving inwards of that zone 

 of the earth which forms the area of depression. Such inward 

 motion must result in the reduction of curvature, and the consequent 

 diminution of area ; in other words, the floor must be contracting 

 and must continue doing so approximately as long as sedimentation 

 proceeds. Thus the only effect of expansion, in such an area, must 

 be in the direction of minimizing the rate of shrinking, and, should 

 the effects of expansion balance those of contraction, the area ceases 

 to sink and deposition soon ends. 



I will now briefly point out what I conceive to be the true 

 phenomena which cause and accompany the deposition of a great 

 thickness of sediment near land. 



Imagine an area, such as I have conceived in the statement of my 

 theory, to be bordered by a large land region. Owing to the more 

 rapid contraction of our depressed area, its floor bends inwards, or 

 the area sinks ; over that portion of the area which borders our 

 supposed land region sediment will be deposited and will accumulate 

 to a greater and greater thickness as the area sinks. This sinking 

 must obviously be accompanied by the actual displacement of 

 material from underneath, which will be forced below the surround- 

 ing regions, and increase their relative height. Thus, as long as 



