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284 ‘DYNAMICAL GEOLOGY. — [Boox IIL 
it never used to touch, should former half-tide rocks cease to be visible 
even at low water, and should rocks, previously above the reach of 
the highest tide, be turned first into shore reefs, then into skerries 
and islets, we infer that the coast-line is sinking. Such kind of 
evidence is found in Scania, the most southerly part of Sweden. 
Streets, built of course above high-water mark, now lie below it, 
with older streets lying beneath them, so that the subsidence is of 
some antiquity. A stone, the position of which had been exactly 
determined by Linneus in 1749, was found after 87 years to be 100 
feet nearer the water’s edge. The west coast of Greenland, for a 
space of more than 600 miles, is perceptibly smking. It has there 
been noticed that, over ancient buildings on low shores, as well as 
over entire islets, the sea has risen. The Moravian settlers have 
been more than once driven to shift their boat-poles inland, some of 
the old poles remaining visible under water.’ Historical evidence 
likewise exists of the subsidence of ground in Holland and Belgium.? 
§ 3. Causes of Upheaval and Depression of Land.—These 
movements must again be traced back mainly to consequences of the ~ 
internal heat of the earth. There are various ways in which 
the heat may have acted. As rocks expand when heated, and 
contract on cooling, we may suppose that, if the crust underneath a 
tract of land has its temperature slowly raised, as no doubt takes 
place round areas of nascent volcanoes, a gradual uprise of the ground 
above will be the result. The gradual transference of the heat to 
another quarter may produce a steady subsidence. Basing on the 
calculations of Colonel Totten, cited on p. 319, Lyell estimated that a 
mass of red sandstone one mile thick, having its temperature augmented 
200° Fahr., would raise the overlying rocks 10 feet, and that a 
portion of the earth’s crust of similar character 50 miles thick, with 
an increase of 600° or 800°, might produce an elevation of 1000 or 
1500 feet.2 Again, rocks expand by fusion and contract on solidifica- 
tion. Hence by the alternate melting and solidifying of subterranean 
masses, upheaval and depression of the surface may possibly be 
produced (see postea, p. 294). 
But processes of this nature can evidently effect changes of level 
only limited in amount and local in area. When we consider the 
wide tracts over which terrestrial movements are now taking place, 
or have occurred in past time, the explanation of them must 
manifestly be sought in some far more wide-spread and generally ~ 
effective force in geological dynamics. It must be confessed, how- 
ever, that no altogether satisfactory solution of the problem has 
’ These observations, which have been accepted for at least a generation past (Proc. 
Geol. Soc. ii, 1835, p. 208), have recently been called in question, but the alleged disproof 
is not convincing, and they are here retained as worthy of credence. See Suess, Verhand. 
Geol. Reichsanstalt, 1880, No. 11. 
* Lavaleye, “ Affaisement du _sol et envasement des fleuves, survenus dans les temps 
historiques,” Brussels, 1859. Grad. Bull. Soc. Géol. France, ii, 83rd ser. p. 46. 
Arends, “ Physische Geschichte der Nordseekiiste,”’ 1833, 
* © Principles,” il. p, 235, 





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