DARWINISM AND EVOLUTION. 1 7 



have, in their turn died, and their hard coverings have been slowly 

 pierced by other creatures, while yet the deposit had not covered 

 the mollusc to half its thickness. Not less slow is denudation. 

 In " faults," when one side of a dislocation has been raised 

 perhaps thousands of feet above the other, and both have been 

 washed down to a level again, though it can be known how 

 much more has been denuded on one side than on the other to 

 restore the level, it cannot be known how much has also been 

 taken from both sides. A fault crossing from Dunbar to the 

 Ayrshire coast, amounts to nearly three miles vertical. This 

 dislocation has on the south side the ancient silurian rocks on 

 which rest the carboniferous. On the north, between the carboni- 

 ferous and the silurian occurs the old red sandstone. So that the 

 dislocation is older than the carboniferous era. For originally the 

 silurian rocks, south of the fault, must have been covered by the 

 prolongation of the old red sandstone, afterwards completely 

 removed by denudation. Thus the enormous thickness of three 

 miles of old red sandstone must have been denuded away during 

 the period which intervened between its deposition and the 

 subsequent accumulation of the carboniferous limestone and coal- 

 measures now lying directly upon the silurian rocks. The quantity 

 of sediment brought down by the Mississippi has been carefully 

 investigated by order of the United States Government, The 

 result is that the mean level of its enormous area of drainage 

 must be lowered 4 5 66 th of a foot annually, or one foot in 4566 years. 

 Mr. Croll, Mr. Geikie,and Sir Charles Lyell consider that denudation 

 takes place at the rate of one foot in 6000 years. Take double this 

 rate, and at two feet in 6000 years the time occupied in denuding 

 three miles of old red sandstone would be 45 millions of years, 

 and this takes no account of the time occupied in deposition. 



But older than the old red sandstones, and before they were 

 deposited, the silurian formations had been denuded to depths of 

 thousands of feet, and these ancient formations were themselves 

 deposited in the ocean by the slow denudation of the Cambrian 

 rocks. These, in turn, had been formed from the earlier Lauren- 

 tian strata ; and the Laurentian rocks themselves were built up 

 from the ruins of other rocks, which were themselves sedimentary 

 rocks, and not the primary rocks of the globe. On the other 

 hand, above the carboniferous, come the Permian, Triassic, Oolitic, 

 Cretaceous, Tertiary, and recent rocks ; the whole amounting in 

 thickness to nearly 14 miles of British strata. Surely then, 

 "sufficiency of time" is less a postulate than a demonstrable 

 fact ; and we are at last fully entitled to claim that the truth of 

 Darwinism is abundantly proved. In other words, the evidence 

 in its favour compels belief. 



But there are two classes of persons whom no amount of 

 evidence will convince. Those who are deeply pledged and 



