SECTIONAL TRANSACTIONS.—C. 375 
by the depth of the original basin unless the basin sinks during the period. The 
position and size of original basins of deposition have been determined, in general, 
by movements of the crust, and their continued existence as areas of sedimentation 
depends on continued depression. In fact, one may almost enunciate a principle— 
no depression, no sediments. 
Further, in the case of clastic sediments, and possibly also in the case of some 
calcareous deposits, a continuing source of supply during a prolonged period depends 
upon upward movement of the neighbouring land area. Ii this ceased to move up 
the ‘ feeding-grounds of erosion’ would be exhausted, so that, in general, we may say 
also, no uplifts, no sediments. 
Some of our most fascinating deposits, e.g. the Jurassic rocks of this country, the 
playground of zonal stratigraphers, owe their interest to the fact that they were formed 
in a nearly filled basin subject to periodic oscillation through a small vertical range. 
On the other hand, we appear to have a close relation between movements and 
sedimentation in those areas where in the past an enormous thickness of deposits 
has formed throughout under shallow water conditions. It has frequently been 
suggested that these areas were depressed in consequence of the weight of sediments 
that were being laid down on that part of the earth’s crust. 
Such an intimate relation between sinking of the crust and the addition of fresh 
load seems to imply an extreme sensitiveness of the crust, and that the maintenance 
of isostatic equilibrium is a rule in such cases. If this be the explanation of the 
relationship it appears to involve the converse possibility, that as material is removed 
from the area adjoining the basin of deposition the land must rise as it becomes 
lightened by erosion. 
Dr. H. Jeffreys has shown that the accumulation of a thick layer of sediments 
exercises some effect upon the thermal conditions at the base of the layer, but this 
does not explain why sedimentation became possible in that particular area in 
preference to others, nor how isostatic equilibrium could have been maintained during 
the accumulation of the first few hundred feet of sediments, 
It appears to me that the dominant control is exercised hy movements of the 
crust. Depression of an area has begun owing to some previous condition of the crust 
and possibly uplift of an adjoining region was simultaneously determined. As soon 
as a basin was formed there appears to have been in the past abundance of material 
available close at hand wherewith to fill it, and the faster it was depressed the faster 
it filled. 
We appear to have no evidence among past sediments of a basin that remained 
unfilled during a long period of continuous depression. 
It is possible, however, that in the Pacific Deeps we have such basins. These are 
so situated as to be either too far for much sediment to reach them or so that there 
is little drainage in their direction from the nearest land areas. It is not improbable, 
however, that the present condition of the crust is somewhat abnormal in respect of 
relief and distribution of land and water and depth of continental shelves as compared 
with past periods. 
In conclusion, I refer briefly to another relation between movements and sedimenta- 
tion which is well known, having been emphasised by Dana, Mellard Reade and others 
many years ago, and more recently by Haug. ‘The relationship is well illustrated by 
our great Paleozoic formations. Intense folding and overthrusting has affected in 
particular those regions of the crust where previously a great thickness of sediments 
had formed. It will be found in general, however, if the level of the foundation on 
which the sediments were laid down is compared before and after the movement, 
that except in very narrow areas it is never raised to the same level after one of these 
violent movements as it occupied before sedimentation began. 
The slow, persistent movements that accompanied the deposition of the sediments 
were of far greater total effect than the more violent and apparently more effective 
folding movements that succeeded the sedimentation phase. 
Prof. E. B. Batery, F.R.S., and Dr. J. We1r.—Submarine Faults as 
Boundaries of Facies. 
The North Sea coast of Sutherland furnishes a wonderful opportunity for studying 
the influence of Kimmeridgian faulting upon contemporaneous sedimentation. The 
exposures belong to the vicinity of a great fault, and illustrate the production of 
boulder beds, coupled with contortions, sandstone-dykes and current phenomena, 
