671 
in terms of projected technological progress in offshore mineral exploi- 
tation. Reasonably interpreted, the Convention definition of the shelf 
extends, and limits, coastal control to adjacent marine regions of suffi- 
cient extent that the outer limit of control will not be reached for a 
very long time. 
As a general rule, the limit of adjacency may reasonably be regarded 
as coinciding with the foot of the submerged portion of the continental 
land mass. There is strong support for this view in the drafting history 
of the Convention,* although other interpretations have been advanced. 
From the geological standpoint, this interface at the submerged conti- 
nental margin is a profound natural boundary. Characterized by a 
marked change of structure between the continental mass and the crust 
of the deep ocean basins, it is generally to be found at a depth of from 
2,000 to 3,000 meters. As stated recently by the United States repre- 
sentative in the Technical and Economic Working Group of the United 
Nations Ad Hoc Committee: 
“The composition of the continents, including their submerged 
parts, is basically different from that of the oceanic crust of the 
deep ocean basins. The boundary between the two is one of the 
most profound natural interfaces. It is gradational. in many places 
and not easily established by direct observation, but generally oc- 
curs near the base of the continental slopes at a depth of about 
2500 meters. 
6 
‘... The gradational interface between the submerged parts of 
the continents and the ocean basins naturally fixes the seaward 
limit of any continental feature, and is from the scientific point of 
view the conceptual boundary between continental and oceanic sea- 
bed resources. It is important to recognize, however, that neither 
this nor any other geologic or topographic boundary is sufficiently 
distinct and consistent to serve by itself as the means of defining a 
precise juridical boundary.” 
In view of the fact that this feature is thus often difficult to locate from 
direct observation, it would seem reasonable and convenient to equate it 
generally, for the time being at least, with the 2,500 meter isobath. This 
would be in approximate accord with the geological realities. 
* See Appendix to this Report. 
