THE EVOLUTIONARY CONCEPT 335 



deposited in his own time off the mouths of the Scottish estuaries. He 

 saw how the storm waves beat against the shore, undermining the sea 

 cliffs and grinding up the boulders that fell from them into sand and 

 mud that joined the other deposits on the bottom. 



Nowhere did Hutton find traces of world-wide cataclysms or of the 

 operation of any processes that could not be seen at work today. It was 

 true that the lands showed evidence that sea-laid sediments, consolidated 

 into rock, had been disrupted, upheaved, and injected with veins and 

 masses of molten rock through the agency of subterranean heat. But 

 these effects had been more or less local and were evidently akin to those 

 produced by present-day volcanoes. Furthermore, earth processes ap- 

 peared to repeat themselves in never-ending cycles. No sooner were new 

 lands uplifted above the sea than atmospheric decay and stream erosion 

 must once more begin to destroy them and make new rock layers from 

 their debris. 



Thus Hutton found evidence everywhere of the slow, long-continued, 

 and orderly working of familiar everyday processes. He was forced to 

 conclude that the geological forces that had been at work in the past 

 were largely the same as those now operative. In a well-worn phrase, 

 "study of the present is the key to the past." This thesis, christened 

 uniformitarianism, is today accepted with but slight modification as a 

 fundamental principle in geology, at least for all that part of earth history 

 during which life has existed. 



Let us pause here to note that the discovery of this principle resulted 

 largely from two qualities of Hutton's work — continued, detailed, and 

 critical observation of natural phenomena, unbiased by preconceptions; 

 and a cautious and sober attitude in attempting to explain the facts 

 thus gathered. It is perhaps significant in this connection that Hutton 

 was Scotch in nationality. He and his followers merely applied in science 

 a rule old in logic but often violated in early geological speculation and 

 even today in ordinary thinking. This is the rule of minimum hypotheses, 1 

 which may be stated as follows: Of all conceivable hypotheses that can 

 be made to explain a given set of facts, those are to be preferred which 

 (1) are most consistent with the data, (2) remove the most difficulties, 

 (3) are simplest, and (4) require the fewest assumptions. The hypothesis 

 (now the principle) of uniformitarianism met these requirements admir- 

 ably, whereas the hypothesis of catastrophism failed to do so. 



Hutton's work at first attracted little attention, partly because the 

 style of his writing was involved and difficult. The wide influence that 



1 Special application of the logical principle enunciated by Duns Scotus and later 

 emphasized by William of Occam (1347 a.d.), after whom it is called "Occam's 

 razor": Entia praeter necessitatem non sunt multiplicanda — "the number of entities 

 should not be increased unnecessarily." 



