PRESIDENT’S ADDRESS—SECTION C. 85 
fluviatile deposits extend far below the sea level. Undoubtedly, 
depression and sedimentation go on together here. The depres- 
sion, however, is not always uniform, for, according to Sir C. 
Lyell, there are unceasing fluctuations in the levels of those areas 
into which running water is transporting sediment. It is also an 
undoubted fact that many series of rocks, sometimes 10,000 or 
even 26,000 feet thick, are made up entirely of shallow water 
deposits ; but here also subsidence has not been continuous. 
Captain Dutton says of the Colorado plateau, “the surface of 
the plateau during Mesozoic times coincided very nearly with the 
sea level, but was constantly oscillating from a little above to a 
little below that level, and wice versa. On the whole, the region 
appears to have subsided about as fast as the sediment accumu- 
lated—thus preserving the surface nearly at a constant level.” 
The same writer says that the tertiary fresh-water deposits round 
the Uinta Mountains are 10,000 feet thick, and “that these beds 
subsided by their gross weight as rapidly as they grew admits of 
no shadow of doubt.” It is also very remarkable that depression 
often takes place along the base of mountain chains just where 
sedimentation has been most rapid. 
On the other hand, the common occurrence of what is known 
as the normal series of deposits shows that subsidence is often 
more rapid than sedimentation, and is not, therefore, caused by 
it. Also extensive subsidence has often occurred without any 
great sedimentation. The mammalian fauna of Madagascar 
proves that that island has been united to Africa since the 
Cretaceous period, but the Mozambique Channel is now more 
than 6000 feet deep. The isolation of many other continental 
islands has, no doubt, been caused by subsidence without sedimen- 
tation, and Mr. Mellard Reade points to the Mediterranean and 
to the Gulf of Mexico as other examples. 
Subsidence and sedimentation, no doubt, often proceed Aarz 
passu; but, as subsidence can take place without sedimentation, 
it seems probable that in some cases the sinking areas may have 
determined the position of sedimentation; and if the rate of 
sedimentation exceeded that of subsidence shallow water would 
be constantly maintained. Also, depression has not always 
followed loading. For example, the 4000 to 5000 feet of lava 
in the Deccan did not depress the land below the sea. It may be 
said that this outpouring of lava without subsidence was due to 
the sinking of some neighbouring area in consequence of a loading 
of still greater weight ; but there is no evidence to favour this 
idea, and it cannot apply to the Sandwich Islands, which are more 
than a thousand miles from any area of sedimentation. Neither 
can it explain the rising of the bed of the Arctic Ocean, notwith- 
standing the detritus brought into it by the great rivers of Siberia. 
In 1865 Mr. T. F. Jamieson proposed to explain the con- 
nection between glaciation and subsidence by the weight of the 
