6 Proceedings of the Royal Physical Society. 
deep sea had been wholly exempt from movement since 
Cambrian times. In fact, the theory of the permanence of 
the deep ocean-basins really demands that the ocean-floor of 
these regions should have been constantly sinking since 
Cambrian times, as otherwise there would have been nothing 
to neutralise the continued accumulation of deep-sea deposits. 
As before said, the doctrine of the permanence of the deep 
oceans carries with it the virtual stability of the great con- 
tinental platforms since Cambrian times, though it allows of 
a large range of vertical displacement as a local and partial 
phenomenon in the latter. Many arguments, both geological 
and biological, of more or less weight, have been brought 
forward in support of this doctrine, and I propose to review 
the more important of these as briefly as possible. Most of 
them may be very shortly dismissed in view of the over- 
whelming importance of one, which, to my mind, is absolutely 
vital. The argument to which I allude is, that if the floors of 
the deep ocean-basins of the present day had ever been raised 
above the level of the sea in times subsequent to the Cam- 
brian, then we ought to find in the existing dry lands some 
deposits which could be fairly compared with the known 
deep-sea deposits of the present day, but that we do not find 
such. This argument is so far vital to the solution of the 
controversy, that though the apparent absence of deep-sea 
deposits in the dry lands would not conclusively prove the 
doctrine of the permanence of the deep ocean-basins, a single 
indubitable instance of the occurrence of such a deposit in 
the dry land would conclusively disprove the doctrine as one 
of universal application; and such instances can, I think, be 
offered in a number of cases. 
The first argument bearing upon the question before us 
which I propose to notice is that of the virtual stability in 
position of the existing continental platforms, as implied in 
the doctrine that our present continents were all sketched 
out in pre-Cambrian times, and have merely been added to 
during successive marginal submergences of small depth. 
This view has been strongly maintained as regards North 
America by Dana, who regards the present exposures of 
Laurentian and other Archzan rocks in North America as 
