lxxxiv PKOCEEDLTS'GS OF THE GEOLOGICAL SOCIETY. [April IQI4, 



forestalled. Determined, however, that his conclusions should be 

 well-founded, he had continued his patient preparation of evidence. 



Wallace at that time had, by his own account, * hardly thought 

 of any serious study of nature.' The idea of natural selection 

 came to him while he was at Ternate, in the Malay Archipelago, 

 in a sudden flash of insight. In a week it was written out and sent 

 to Darwin. Darwin, forestalled after 20 years of work, maintained 

 that Wallace was entitled to an equal share with himself in the 

 honour of the discovery ; Wallace himself considered that his share 

 might be estimated in the proportion of one week to twenty years. 

 In 1858 joint papers by Darwin and Wallace, ' On the Tendency 

 of Species to form Varieties, & on the Perpetuation of Varieties 

 & Species by Natural Selection,' were communicated to the Linnean 

 Society. This, briefly, is the story of the birth of a theory on 

 which modern biology and pala3ontolog} r are based. 



Both the great men who took part in this contest of magnanimity 

 have now passed away, but before his death Wallace received proof 

 of the high value which was to be attached by posterity to his 

 work and to his share in the discovery. 



One of the subjects touched upon by Wallace was an estimation 

 of the age of the Earth. In discussing calculations founded on the 

 length of the stratigraphical column, he pointed out that, although 

 denudation proceeds on all exposed land-surfaces, deposition is 

 confined to the coastal parts of the oceans, and is correspondingly 

 more rapid. After careful consideration of the limits of the area 

 within which the degraded material may be assumed to be distri- 

 buted, he inferred that 



' deposition, as measured by maximtim thickness, goes on at least nineteen 

 times as fast as denudation.' 



On the strength of this conclusion he advocated a large reduction 

 in the estimate of time required for the deposition of the strata of 

 the world. The conclusion may be well-founded, but it helps little 

 if our knowledge of the rate of denudation is confined to mere 

 guesses ; and it must be admitted that our knowledge, not only as 

 regards the rate at which any one of the many types of existing 

 land-surface, but, still more, the land-surface of the globe as a 

 whole, are being degraded, deserves no better description. 



