The Continental Platform 
which open out on the floor of the abyssal ocean at the above or greater depths, as will be shown later 
on: for the present it is only necessary to record the fact. 
Mode of Formation of the Continental Platform and accompanying Shelf.—In dealing with this problem we 
have to recognise that the land of the northern hemisphere has undergone enormous changes of level in 
Pliocene and Pleistocene times—changes of elevation and depression, and of elevation again ; this will be 
abundantly proved in subsequent chapters, when we come to consider the phenomena of the submerged river- 
valleys. The floor of the Shelf was at one time a land surface as shown by the river channels by which it 
is traversed, which could never have been formed under the waters of the ocean itself,’ and the Continental 
Slope constituted the coast line of the ocean at various stages of elevation and depression. During this 
process of terrestrial movement there were doubtless pauses, when the surface of the Platform was swept 
by the Atlantic waves ; and the Continental Shelf was the outcome mainly of wave action and erosion 
on the one hand, and on the other of the action of atmospheric denudation, where the rains, rills, and 
streams have reduced the coastal plains to levels of no erosion; in either case, submerged terraces or 
platforms result upon the sinking of the land or rise of the ocean level. The Continental Slope, formed to 
some extent of terraces hewn out of the rock as the land rose or fell, assumed its present form somewhat as 
do the now emergent cliffs on our rock-bound coasts of Norway, Scotland, and Ireland. Such, in general 
terms, appears to have been the process by which the submerged features were formed. It involves a 
recognition of a great lapse of time, which is difficult for the mind to realise, especially at so recent a 
stage of the world’s history ; nevertheless the evidence appears conclusive that, given the necessary time, 
these great terrestrial results have been accomplished mainly by wave action on the lands during 
periods of elevation and depression, accompanied by occasional pauses giving rise to terraces. 
We must not, however, lose sight of the fact that very different views regarding the origin of the 
continents and deep oceans have been held by eminent men, and they ought not to be passed over without 
due consideration. There have existed two principal schools of geographical evolution, and of the 
theories regarding the permanence or non-permanence of the greater features of the earth’s crust. Under 
the former view, the depths of the ocean, as also the position of the chief continental areas, retain traces 
of their primeval structure, and. have been only slightly modified by subsequent events. Thus, Lord 
Kelvin held the view that continents and ocean depths were due to differences of composition in different 
parts of the liquid matter which constituted the earth’s surface before solidification, and from this 
heterogeneousness he considered that the irregularities of the present surface followed as a dynamical 
necessity. According to the latter view, which is that held by the author, the land and the sea have at 
various geological periods changed places ; and this can be demonstrated by considerations based on the 
distribution of the geological formations on both sides of the North Atlantic Ocean. 
In a paper which was read by the author before the Geological Society some years ago,” it was shown 
how the strata constituting the Carboniferous and Mesozoic formations become attenuated when traced 
from their north-westerly margins towards the south-east of England; or, in other words, swell out in 
thickness towards the Atlantic coast—a view supported by the results of the Geological Survey. These 
strata being in nearly every case of marine origin, it was inferred that the sediments of which they are 
composed must have come from lands lying in a direction towards which they augment in thickness ; in 
other words, the North Atlantic Ocean. On the other hand, Sir C. Lyell, when treating of the distribu- 
tion of the Carboniferous rocks of North America, shows that the sedimentary strata increase in thickness, 
and become coarser in texture, as they approach the north-eastern seaboard ; attaining in Nova Scotia, 
according to Dawson, a thickness of 14,000 feet. The conclusion, therefore, which has been drawn from 
1 In order to understand the argument underlying the conclusions adopted in this work, the reader is supposed to understand that rivers and 
river-valleys cannot be formed under the waters of the ocean. The effect of these waters is to retard and ultimately to destroy the eroding action 
of the streams on entering the sea. 
2 “On the South-Easterly Attenuation of the Lower Secondary Formations of England,” Journ. Geol. Soc. vol. xvi. (1860). 
3 Dawson, Acadian Geology. 
