CHAP. VI GEOGRAPHICAL AND GEOLOGICAL CHANGES 87 



If we now examine the stratified rocks found in the very- 

 centre of all our great continents, we find them to consist 

 of sandstones, limestones, conglomerates, or shales, which 

 must, as we have seen, have been de23osited within 

 a comjDaratively short distance of a sea-shore. Sir 

 Archibald Geikie says : — " Among the thickest masses of 

 sedimentary rock — those of the ancient Palaeozoic systems 

 — no features recur more continually than the alternations 

 of different sediments, and the recurrence of surfaces 

 covered with well-preserved ripple-marks, trails and 

 burrows of annelides, polygonal and irregular desiccation 

 marks, like the cracks at the bottom of a sun-dried muddy 

 pool. These phenomena unequivocally point to shallow 

 and even littoral waters. They occur from bottom to top 

 of formations, which reach a thickness of several thousand 

 feet. They can be interpreted only in one way, viz., that 

 the formations in question began to be laid down in shallow 

 water; that during their formation the area of deposit 

 gradually subsided for thousands of feet ; yet that the rate 

 of accumulation of sediment kept pace on the whole with 

 this depression ; and hence that the original shallow-water 

 character of the deposits remained, even after the original 

 sea-bottom had been buried under a vast mass of sedi- 

 mentary matter." He goes on to say, that this general 

 statement applies to the more recent as well as to the more 

 ancient formations, and concludes — "In short, the more 

 attentively the stratified rocks of the earth are studied, the 

 more striking becomes the absence of any formations amoug 

 them, which can legitimately be considered those of a deep 

 sea. They have all been deposited in comparatively 

 shallow water." ^ 



The arrangement and succession of the stratified rocks 

 also indicate the mode and place of their formation. We 

 find them stretching across the country in one general 

 direction, in belts of no great Avidth though often of immense 

 length, just as we should expect in shore deposits ; and 

 they often thin out and change from coarse to fine in a 

 definite manner, indicating the position of the adjacent land 



1 Geographical Evolution. {Proceedings of the Royal Grngrajthical Society. 

 1879, p.' 426.) 



