798 REPORT—1899. 
the bases leached out of the disintegrating rocks are carried out into the ocean 
and ocean-basins, A continuous disintegration and differentiation of materials of 
the lithosphere, accompanied by a sort of migration and selection among mineral 
substances, is thus always in progress. Through the agency of life, carbonate of 
lime accumulates in one place; through the agency of winds, quartz sand is heaped 
up in another; through the agency of water, beds of clay, of oxides of iron and 
of manganese are spread out in other directions. 
The contraction of the centrosphere supplies the force which folds and crumples 
the lithosphere. The combined effect of hydrosphere, atmosphere, and biosphere 
on the lithosphere gives direction and a determinate mode of action to that force. 
From the earliest geological times the most resistent dust of the continents has 
been strewn along the marginal belt of the sea-floor skirting the land. At the 
present time the deposits over this area contain on the average about 70 per cent. of 
free and combined silica, mostly in the form of quartz sand. In the abysmal 
deposits far from land there is an average of only about 30 per cent. of silica, and 
hardly any of this inthe form of quartz sand. Lime, iron, and the other bases largely 
predominate in these abysmal regions. The continuous loading on the margins of 
the emerged land by deposits tends by increased pressure to keep the materials of 
the tektosphere in a solid condition immediately beneath the loaded area. The 
unloading of emerged land tends by relief of pressure to produce a viscous 
condition of the tektosphere immediately beneath the denuded surfaces. Under 
the influence of the continuous shakings, tremors, and tremblings always taking 
place in the lithosphere the materials of the tektosphere yield to the stresses acting 
on them, and the deep-seated portions of the terrigenous deposits are slowly carried 
towards, over, or underneath the emerged land. The rocks subsequently re-formed 
beneath continental areas out of these terrigenous materials, under great pressure 
and in hydrothermal conditions, would be more acid than the rocks from which 
they were originally derived, and it is well known that the acid silicates have a 
lower specific gravity than the intermediate or basic ones. By a continual repeti- 
tion of this process the continental protuberances have been gradually built up of 
lighter materials than the other parts of the lithosphere. The relatively light 
quartz, which is also the most refractory, the most stable, and the least fusible 
among rock-forming minerals, plays in all this the principal ré/e. The average 
height of the surface of the continents is about three miles above the average level 
of the abysmal regions. If now we assume the average density of the crust 
beneath the continents to be 2°5, and of the part beneath the abysmal recions to 
be 3, then the spheroidal surface of equal pressure—the tektosphere—would have a 
minimum depth of eighteen miles beneath the continents and fifteen miles beneath 
the oceans, or if we assume the density of the crust beneath the continents to be 
2'5, and beneath the abysmal regions to be 2°8, then the tektosphere would be 
twenty-eight miles beneath the continents and twenty-five miles beneath the 
oceans. The present condition of the earth’s crust might be brought about by the 
disintegration of a quantity of quartz-free voleanic rock, covering the continental 
areas to a depth of eighteen miles, and the re-formation of rocks out of the 
disintegrated materials. 
Where the lighter and more bulky substances have accumulated there has been 
a relative increase of volume, and in consequence bulging has taken place at the 
surface over the continental areas, Where the denser materials have been laid 
down there has been flattening, and in consequence a depression of the abysmal 
regions of the ocean-basins. It is known that, as a general rule, where large 
masses of sediment have been deposited, their deposition has been accompanied 
by a depression of the area. On the other hand, where broad mountain platforms 
have been subjected to extensive erosion, the loss of altitude by denudation has 
been made good by a rise of the platform. This points to a movement of matter 
on to the continental areas. 
If this be anything like a true conception of the interactions that are taking 
place between the various geospheres of which our globe is made up, then we can 
understand why, in the gradual evolution of the surface features, the average 
level of the continental plains new stands permanently about three miles above 
