THE PLAN OF THE EARTH AND ITS CAUSES. 1 



By J. W. Gregory, D. Sc. 



THE VARIATIONS OF TOPOGRAPHIC FORM. 



Despite the extreme variability in the shapes of the continents and 

 their apparently capricious distribution, geographers of all ages have 

 believed that the arrangement of land and water on the globe is based 

 on a regular plan. The plan can, of course, only be recognized in 

 broad outline, for the shape of the land masses depends on the struc- 

 ture of the earth forms, which vary indefinitely. Intricate mountain- 

 valley systems open out to wide-flung rolling prairie, stoneless alluvial 

 flats are broken by the crags of rock ridges, volcanic cones stand 

 isolated like pyramids, while mountain chains run thousands of miles 

 unbroken. Such contrasts are natural, as the land forms are the result 

 of the struggle of complex forces with varying powers of attack against 

 complex rock masses formed of materials having varying powers of 

 resistance. Coast lines, for example, project where hard rocks repel 

 the surf, where rivers deposit alluvium more quickly than the tide can 

 remove it, or where the winds build up sand dunes, whose very weakness 

 disarms the waves. Coast lines are indented where soft beds crumble 

 under frost and rain, and where dominant winds, the inset of an ocean 

 current, or an undulation on the sea floor directs a jet-like stream of 

 water against the shore. Topographical form depends on so many 

 incalculable, inconstant factors that the stages of its growth are often 

 now untraceable. The missing links of geographical evolution are 

 indeed as numerous as those of organic evolution, and the chapter of 

 accidents is invoked by geographers to explain difficulties analogous 

 to those for which naturalists appealed to the doctrine of special crea- 

 tion. But unexplained differences in the geographical units no more 

 disprove an orderly progress in the growth of the continents than the 

 existence of isolated, unexplained groups of animals is fatal to Dar- 

 winism. Such topographical differences are of secondary importance 

 in contrast to the numerous coincidences and repetitions of the same 

 essential form among the geographical units. Geographers accordingly 



1 Read at the Royal Geographical Society, January 23, 1899. From The Geograph- 

 ical Journal, No. 3, March, 1899, Vol. XIII, pp. 225-251. 



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