DIASTROPHISM AND THE FORMATIVE PROCESSES — 195 
overmantlings of large fractions of the face of the continents by 
marine deposits in Ordovician, Silurian, Cretaceous, Eocene, and 
other periods. Without such relatively static periods general base- 
leveling seems impossible. ‘Theoretically such periods are assign- 
able to previous effective easement of all differential stresses of the 
higher order. Such easement is really implied in the emergent state 
of the continents and the reciprocal depressed state of the great 
basins just assumed as the first stage in the case we are following. 
3. During this relatively quiescent period let the normal pro- 
cesses of denudation and deposition follow their inevitable courses, 
unloading the continents and loading the ocean basins, while the 
sea slowly encroaches upon the borders of the continental platforms 
until, let us say, 30 per cent or 4o per cent of the surface of the 
continental platforms is overlipped by the thin edges of the oceans. 
Among the incidents of this period the following may be noted: 
a) In the early stages the bordering belts of the continents, 
as a rule, suffered greater relative unloading than the interiors 
because they had been most affected, on the average, by the pre- 
ceding diastrophism, and their drainage gradients were higher than 
those of the more remote interior and the denudation more rapid, 
while the direct action of the cutting edge of the sea added its 
effects. 
b) Later in the period, as the sea crept forward over the widen- 
ing shelf and gave rise to the deposition of top-set beds upon the 
surface of the shelf, the weight of these deposits compensated in 
some measure for the previous unloading, while the rise of the sea- 
level itself, due to the sediment carried into the oceans, added some 
further compensation by an increasing burden of sea-water. 
c) The mechanical sediments from the land, beside lodging on 
the sea-shelf as top-set beds, accumulated predominantly around 
the shelf-edge as fore-set beds, while subordinately they were carried 
farther out to sea and settled widely over the ocean bottom. 
d) The solvent material was at first distributed by currents 
and diffusion with approximate uniformity throughout the oceanic 
waters, but later a part of it was extracted by organic and other 
agencies and deposited wherever chance overtook it, often far from 
its point of origin on the continent. 
