
454 _ DYNAMICAL GEOLOGY. —_[Boox IIE. 


action of the sea, are deceptive. In Fig. 166, one of innumerable — 
examples from the Old Red Sandstone cliffs of Caithness and the — 
Orkney and Shetland Islands, we at once perceive that the process 
of demolition is precisely similar to that already cited in Fig, 164, 
The cliff recedes by the loss of successive slices from its sea-front, 
which are wedged off not by the waves below, but by the subaerial 
agents above, along lines of parallel joint. To the inclination of 
these divisioral planes at a high angle from the sea, the precipice 
owes its slope towards the land. 


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Fic. 166.—Overnancine Ciirr, Broucu or Birsa, ORKNEY. 
Ice erosion—Among the erosive operations of the sea must be 
included what is performed by floating ice. Along the margin of 
Arctic lands a good deal of work is done by the broken-up floe-ice 
and ice-foot. These cakes of ice, driven ashore by storms, tear u 
the soft shallow-water or littoral deposits, rub and scratch the rocks, 
and push gravel and blocks of rock before them as they strand on 
the beach. Icebergs also, when they get aground in deep water, 
must greatly disturb the sediment accumulating there, and may 
grind down any submarine rock on which they grate as they are 
driven along. ‘The geological operations of floating ice were 
formerly invoked by geologists to explain much that is now believed 
to have been entirely the work of ice on land. 
(3.) Transport.—By means of its currents the sea transports 
mechanically suspended sediment to varying distances from the land. 
The distance will depend on the size, form, and specific gravity 
of the sediment on the one hand, and on the velocity and transporting 
power of the marine current on the other, Babbage oatitnatal 
that if from the mouth of a river 100 feet deep, suspended limestone 
