THE ULTERIOR BASIS OF TIME DIVISIONS 453 
has been reduced. Aside from this, so far as I can See, our 
argument holds as firmly for 1elative as for absolute sinking. 
From the greater depths to which the ocean bottoms have 
sunk, the presumption follows that in every great crustal read- 
justment the major factor consisted of the descent of the ocean 
bottom or some part of it. Logically, as here stated, this is 
only a presumption which might be set aside by the assumption 
of a single or a few great depressions, while the other move- 
ments might be upward or indifferent, but this will appear less 
tenable in the light of further considerations. 
Not only has there been increase in depth, but increase in 
capacity also. From a capacity essentially zero at the outset 
the basins have developed a capacity sufficient to hold nearly all 
the water of the globe. In the aggregate, therefore, the capaci- 
ties of the ocean basins, as well as their depths, have been 
increased by crustal readjustment, and the presumption is that 
this has usually been the case in individual readjustments, 
although this does not rigorously follow. It will be sustained, 
however, by further considerations. The crustal readjustments 
here referred to are those resulting from internal causes. Exter- 
nal readjustments work to precisely opposite ends, the degrada- 
tion of the land and the filling of the basins. This opposing 
action strengthens the presumption that the internal causes have 
habitually increased the capacity of the basins, for they have 
grown more and more capacious in spite of this constantly 
opposing action. This constant filling in affords a presumption 
of frequently repeated increases of capacity ; otherwise the land 
should have disappeared. 
Proceeding upon the presumption that internal readjustments 
habitually increased the capacity of the ocean basins, it is 
important to note in detail the consequences that follow. These 
are involved in the functions of the’ circumcontinental terrace, 
and will be more easily followed after an explicit statement of 
these functions. These are more or less fully apprehended by 
all acute students of continental evolution, but like the correla- 
tive functions of baseleveling previous to the explicit exposition 
