CHAP. VI.] GEOGRAPHICAL AND GEOLOGICAL CHANGES. 



85 



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 in- 

 terpreted 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 sedimentary 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 among 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 width 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 from the dShris of which they 

 were originally formed. Again quoting Professor Geikie : — 

 " The materials carried down to the sea would arrange them- 

 selves then as they do still, the coarser portions nearest the 

 shore, the finer silt and mud furthest from it. From the 

 earliest geological times the great area of deposit has been, 

 as it still is, the marginal belt of sea-floor skirting the land. 



^ Geographical Evolution. {Proceedings of the Royal Geographical Society^ 

 1879, p. 426.) ' : 



