132 THE QUESTION OF WORKABLE 



would make this article unreadable to the general public. Such axes 

 of elevation as have been referred to are, however, but mere wrinkles 

 on the larger curvatures of the lithosphere of the globe ; while in 

 some cases, as in the broad arch of the Rocky Mountains, the later 

 stratified rocks still form a vast plateau, which may some day be 

 thrown into the form of a normal mountain-chain, when the deep 

 incisions made by the canons shall relieve the strain sufficiently to 

 allow the rocks below to be ridged up into another crystalline axis. 



We must free our minds of the popular fallacy that the stratified 

 rocks of the globe are parts of what were once continuous layers 

 spread over the globe. All recent progress in geological science has 

 led to the recognition of the fact that they were definitely related to 

 the older continental masses, off the margins of which they were 

 deposited, from which also their materials were in great part derived 

 by the ordinary processes of waste and transport by water. This was 

 first, I believe, prominently put forward in this country by Professor 

 Geikie, in his presidential address to the Geographical Section of 

 the British Association at Edinburgh in 1892, though to some of us 

 who were familiar with the Continental literature of the subject, there 

 was nothing new in it. 



Now the question naturally arises as to whether geology affords 

 any evidence of the stage in the earth's history at which " dry 

 land " was first formed by elevation above the once universal ocean. 

 This has been often considered and debated. For my own part 

 I am inclined to the view which I have put forward elsewhere, 

 and which is held by some geologists whose views are entitled to 

 respect, that we have no evidence . of any general land elevation 

 before what is known as the Devonian age, when we meet with first 

 appearances of a definite land-vegetation, the anthracite and 

 graphite of the earlier strata being derived from marine Algaj.'' All 

 the formations of previous date (the sandstones, the conglomerates, 

 the mudstones, the limestones, and the clays since altered into slates), 

 of the Cambrian and Silurian periods, are of the nature of marine 

 deposits, as testified by their fossil contents ; and where these fail 

 us, as in the Cambrian and Huronian conglomerates and sand- 

 stones (altered m many cases into quartzites), the occurrence of 

 such strata is perhaps best explained by the enormous tidal action 



3 That is to say, the earlier stratified sedimentary rocks. The graphite of the Archasan rocks 

 h.-xd in all probability a different origin altogether, and had nothing to do with plants, but was of 

 mineral origin, as I have shown op.cit., and in a paper read at the Bath meeting of the British 

 .Association, i8S8. 



