Geology. — “On the Relation between the Pleistocene Glacial Period 
and- the Origin of the Sunda Sea (Java- and South China- 
Sea), and its Influence on the Distribution of Coralreefs 
and on the Land- and Freshwater Fauna”. By Prof. G. A. F. 
MoOLENGRAAFF and Prof. Max Wesrr. 
(Communicated at the meeting of November 29, 1919). 
I. GEOLOGICAL PART by G. A. F. MorENGRAAFF. 
The continental shelves and the agents at work in their formation. 
It is a well-known fact that continents are encircled over large 
distances by shallow seas deepening gradually down to about 100 
fathoms. Farther seaward this depth progresses more rapidly, until 
the average ocean-depth is attained. 
The floors of those shallow seas are together known by the com- 
prehensive name of “the continental shelf”. The total area of this 
shelf is according to Murray about 25 million km.*. 
In most textbooks the way in which the continental shelves ori- 
ginate is seldom explained, and their existence is generally put 
forward without comment as something quite natural. Moreover 
in the European geological literature the problem of their origin 
belongs to the more or less neglected subjects. This is the more 
remarkable since the existence or the non-existence of shelves and 
the manner in which they develop is apt to throw much light upon 
the geological history of the region concerned. 
Shelves must arise along the borders of every continent as long 
as its position relative to the sea-level remains constant; then the 
shelf is built up and enlarged by the sediments transported to the 
sea through the various denuding agents ') which act upon the land ®). 
The more denudation progresses, the more it becomes obvious that the 
1) Including the action of the surf, i.e. the abrasion at the coasts, and the 
formation of the plane of abrasion. . 
2) As long as the position of the land relative to the sea remains stable, the 
area of the shelf will grow towards the sea. Towards the land, however it will 
lose ground, because the peneplain not only broadens towards the land with 
increasing denudation, but also in some degree encroaches upon the shelf through 
accretion. 
26 
Proceedings Royal Acad. Amsterdam. Vol. XXIII. 
