397 
all. Very often, however, diastrophism introduces a new cycle of 
erosion, and consequently revives the process of denudation, resulting 
in the long run in intensified gradation and in growth of the con- 
tinental shelf. 
A lapse of time succeeding a period of strong diastrophism 
will, for regions affected by this process, be characterized 
by potent denudation, active sedimentation and a corresponding 
strong development of the gradation-plane, consequently also of 
the continental shelf. 
2nd. Negative movement of the coastline, i.e. uplift of the land 
or lowering of the sea-level will, as a direct consequence, narrow 
the continental shelf, or cause it to disappear altogether, expanding 
the emerged portion of the gradation-plane at the cost of the sub- 
marine portion. But, on the other hand, such a movement will in- 
vigorate the erosion by lowering the baselevel and will, there- 
fore, in the long run promote the growth of the continental shelf 
indirectly. 
3rd, Positive movement of the coastline, i.e. subsidence of the 
land or rise of the sea-level, will eo ipso broaden the continental 
shelf by expansion of the submerged portion of the gradation-plane 
at the cost of the emerged portion, although in the long run its growth 
will be slackened on account of the baselevel being raised. Even in 
case, at the commencement of such a positive movement, the terres- 
trial portion of the gradation-plane is little developed, or wanting, 
circumstances are imaginable in which the shelf will grow to a 
large extent. This will occur during a very slow but prolonged rise 
of the sea-level. In this case the sea, even if the land should offer a 
strong resistance, will be able to conquer a vast territory, to destroy 
the land down to the plane of abrasion, and to incorporate the 
latter with the shelf. A small island may be altogether truncated 
and converted into a very shallow submarine bank, probably gently 
inclining towards the side where the influx of the sea came from 
i.e. from where the prevailing winds were blowing. 
It stands to reason that, during a positive movement, the above 
extension of the continental shelf will be more rapid and far-reaching 
in case this movement has been preceded by a period of stability 
of the land, in other words by a period of peneplanation. For in 
that case the sea needs not gradually destroy and clear away 
the land in order to form a plane of abrasion and to incorporate 
it into the shelf; on the contrary, it finds a peneplain ready made, 
i.e. a vast area of low land easy to invade and to convert into 
a shelf. 
. 26% 
