The Plan of the Earth and its Causes. — Gregory. loi 
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 thou- 
sands 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 dom- 
inant 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, 
inconsistent 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 creation. But unexplained differ- 
ences 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 Darwinism. 
Such topographical differences are of secondary importance 
in contrast to the numerous coincidences and repetitions of 
the same essential form among the geographical units. Geog- 
raphers accordingly have believed that there is a hidden con- 
tinental symmetry which, when discovered, will explain the 
law that has determined the distribution of land and water on 
the globe. 
This idea dates from the dawn of geographical science. 
The early classical geographers noticed how the seas radiated 
from the Levantine area, and opened to a broad boundless 
ocean. They accordingly described the land of the globe as an 
island, floating on a vast surrounding sea, whence channels 
converged towards the hub of the classical universe. This 
radial plan reappears in the mediaeval wheel-maps, in which 
Jerusalem was accepted as the center of the world, whence the 
main geographical lines radiated like the spokes of a wheel. 
