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 .” 1 
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 debris 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. 
1 Geographical Evolution. (. Proceedings of the Royal Geographical Society. 
1879, p.426.) 
