t 
12 COSMICAL ASPECTS OF GEOLOGY. [Boo I. 
The polar flattening, established by measurement and calcula- 
tion as that which would necessarily have been assumed by an 
originally plastic globe in obedience to the movement of rotation, 
has been cited as evidence that the earth was once in a plastic 
condition. Taken in connection with the analogies supplied by 
the sun and other heavenly bodies, this inference seems well 
grounded.’ | 
Though the general spheroidal form of our planet, and possibly the 
general distribution of sea and land, are referable to the early effects 
of rotation on a fluid or viscous mass, it is certain that the present 
details of its surface-contours are of comparatively recent date. 
Speculations have been made as to what may have been the earliest 
character of the solid surface, whether it was smooth or rough, and 
particularly whether it was marked by any indication of the 
existing continental elevations and oceanic depressions. So far as 
we can reason from geological evidence, there is no proof of any 
uniform superficies having ever existed. Most probably the first 
formed crust broke up irregularly, and not until after many successive 
corrugations did the surface acquire stability. Some writers have 
imagined that at first the ocean spread over the whole surface of the 
planet. But of this there is not only no evidence, but good reason 
for believing that it could never have taken place. As will be alluded 
to in a later page, the preponderance of water in the southern 
hemisphere seems to indicate some excess of density in that 
hemisphere. ‘This excess can hardly have been produced by any 
change since the materials of the interior ceased to be mobile; it 
must therefore be at least as ancient as the condensation of water on 
the earth’s surface. Hence there was probably from the beginning 
a tendency in the ocean to accumulate in the southern rather than 
in the northern hemisphere. 
That land existed from the earliest ages of which we have any 
record in rock-formations, is evident from the obvious fact that these 
formations themselves consist in great measure of materials derived 
from the waste of land. When the student in a later part of this 
volume is presented with the proofs of the existence of enormous 
masses of sedimentary deposits even among some of the oldest 
geological systems, he will perceive how important must have been 
the tracts of land that could furnish such piles of detritus. 
The tendency of modern research is to give probability to 
* It has been recently opposed, however, by Mohr (Geschichte der Erde, p. 472) 
who, adopting a suggestion long ago made by Playfair, hag endeavoured to show that 
the polar flattening can be accounted for by greater denudation of the polar tracts 
exposed as these have been by the heaping up of the oceanic waters towards the equator 
in consequence of rotation. He dwells chiefly on the effects of glaciers in lowerin 
the land, but as Pfaff has pointed out, the work of erosion is chiefly performed by other 
atmospheric forces that operate rather towards the equator than the poles (Allgemeine 
Geologie als exacte Wissenschaft, p. 6). Compare Naumann, Neues Jahrb. 1871, p. 250. 
Nevyerthelss, Mohr has undoubtedly recalled attention to a conceivable cause by which 
in spite of polar elevation or equatorial subsidence, the external form of the planet 
might be preserved. 


