DYNAMICAL GEOLOGY 
89 
tonic significance of relief expression. Relation of sea and land 
is made casual and essential instead of merely accidental and 
trivial. Consequently the geographic definition of_ continent is 
really meaningless. 
Instead of distinguishing between continental platforms and 
oceanic depressions, a circumstance imposed by an unweening 
importance attached to the presence of the sea — a notion handed 
down from time immemorial — the proper discrimination to be 
made is between the continental ridges of the continental borders 
and the intervening lowlands whether above the level of the waters 
in the continental interiors or beneath sea-level as in the oceanic 
areas. On this basis the tracts which we are accustomed to des¬ 
ignate the oceanic depressions and the sea-level interiors of the 
continents are arranged in the same taxonomic category. Consid¬ 
eration of any such datum plane as sea-level may be with full 
propriety entirely neglected. The meridional disposition of the 
continents thus comes to be readjusted as relatively narrow 
orographic ridges in place of broad basin-shaped plateaus. 
The tectonic consideration of a waterless earth casts a new light 
upon the schematic form of our globe. In its logical conse¬ 
quences the contractional hypothesis finds expression in such 
figments of the imagination as the reseau pentagonal of Elie de 
Beaumont, and the tetrahedral globe of Lothian Green. To be 
sure the form known as the tetrahedron is of all geometric 
solids the one form which possesses the least volume in compari¬ 
son with a given surface area, while the sphere contains the 
greatest bulk within the same surface; yet the collapse of the 
latter is not necessarily any such crystallographic shape as that 
indicated by the former. 
In the present state of our knowledge and schematic form 
of our earth is largely conjectural. However, it is suggested lately 
that in the case of a collapsing spheroid the initial tendency to¬ 
wards a faceted form would probably not be directly in the line 
of any limiting shape as a four-sided figure, but towards some¬ 
thing intermediate, between a limiting shape and the most general 
form, or a figure having twelve or twenty-four faces. That the 
rhombic dodecahedron is possibly the real plan, if there be any, 
although having in nature curved surfaces, seems to be borne 
out by the trend of the chief mountain ranges of the world, and 
