HAS THE DEEP OCEAN EVER BEEN LAND? 407 
“permanence of oceanic areas,” would represent their views more 
correctly than “ permanence of continental areas.” 
_ The oldest known rocks of the Laurentian series are formed 
from the detritus of other rocks which had already been worn 
away by denudation ; consequently land must have existed even 
then. But it is not until we arrive at the Silurian period that 
we find remains of land plants and animals. At this time ferns 
and Lepidodendra existed. In rocks of the Devonian period 
we find freshwater shells belonging to a genus at present living 
in our rivers ; and in the Carboniferous period there were insects 
and land shells, the latter closely related to living species. As 
these forms are doubless the progenitors of those now living, it 
follows that since the Silurian period land has always existed on 
the surface of the earth. In order to explain this continuance of 
land we may suppose (1) that the continental areas, once formed, 
have remained the same, and have never been entirely sub- 
merged ; or (2) that when subsidence of land below the sea 
took place on a large scale, it was compensated by the elevation 
of portions of the ocean bed into land ; or (3) a combination of 
both, some small areas never having been submerged, and some 
oceanic areas having at one time been land. 
When we consider the great depth of the oceans, it becomes 
evident that movements of elevation or subsidence, which would 
ereatly alter the shape of a continent, would produce no apparent 
effect if they took place in the deep ocean. The average depth 
of the North Pacific is 15,850 feet ; of the North Atlantic 14,000 
feet; andof the South Pacificand South Atlantic about 13,000 feet. 
But great as are these depths, we have proofs that the surface of 
the earth undergoes upheavals to an equal amount. Marine 
rocks of Eocene age are found in the Pyrenees and Alps at ele- 
vations of 10,500 feet, and in Western Thibet at 16,500 feet. 
Corals belonging to still living species are found fossil at a height 
of 3000 feet at Peru, and Lake Titicaca, 12,500 feet above the 
sea, contains marine forms of crustacea, one of which (Allorchestes 
imermzs) lives also in the Straits of Magellan. Evidently, then, 
the forces which mould the contours of the earth’s surface are 
sufficiently powerful to lift the oceanSbed up into the air ; but, 
of course, it does not follow that they have done so. Let us ex- 
amine the evidence. 
The sedimentary rocks which form the land are all shallow 
water deposits, occurring as long narrow strips, rarely, if ever, a 
hundred and fifty miles wide. They are conglomerates, sand- 
stones, clays, and limestones, such as are forming along the sides 
of the continents at the present day; while the deep water de- 
posits now forming are either calcareous ooze with abundance of 
Foraminifera, especially the form called Globigerina; or, if 
below 15,000 feet, are of red clay. These deposits show no ten- 
dency to take a linear shape like the rock formations forming 
the land. The only exception to this statement is, perhaps, the 
chalk of Europe, which once extended from Ireland to the Cri- 
mea and from Sweden to the South of France, and is composed 
