numbers; at the same time the Lamellibranchiate Mollusca became more predominant. Dry land appeared further south, as evinced by the lignite and freshwater beds intercalated in the Cretaceous series of Southern France. At the close of this period the continent of Europe may have acquired larger dimensions, although it was not until after the great Nummulitic sea of Lower Eocene age (which also stretches through southern Europe to India) had become in part dry land that the "relief" of the continent approximated to that of the present day. On the western edge of the new land formed by the elevation of a portion of the old Chalk ocean more littoral deposits then began to form; and the same thing took place on the sea-belt of the American continent.
The Cretaceous formation of the south-west of England and west of France and north of Ireland passes out under the Atlantic, and reappears on the south-east coast of the North-American continent. As it thus trends in the same direction on both sides of the Atlantic, there would be nothing improbable in supposing that old Cretaceous ocean prolonged further in the same given direction across the present Atlantic.
It is well known that at a distance varying from 50 to 200 miles off the coasts of western Europe, the sea-bed deepens rapidly to 600, then to 1200 feet, and again almost suddenly to depths of from 6000 to 15,000 feet. Does this mark a boundary of the materials drifted out to sea during Postcretaceous times? or is it a line of still older date?
The great and distinctive feature of the Tertiary series is that, with few exceptions, the whole of them were deposited in shallow seas. The London Clay even, which is from 400 to 500 feet thick, does not represent a sea-bed deep in proportion, as there is evidence to show that it was probably deposited during a period of gradual depression of the sea-bed. The total thickness of all the English Tertiaries does not exceed 2000 feet, or that of the Paris-basin Tertiaries 1500 feet[1]. Therefore, while the deep Atlantic area continued submerged, movements of elevation and depression affecting the continental European area (leaving out the changes during the Glacial period) may have gone on during the Tertiary period to the extent of from 2000 to 5000 feet, leaving abyssal depths of from 10,000 to 12,000 feet unaffected by these movements, even supposing they extended over the oceanic as well as the continental area. It is the same on the American coast of
- ↑ Though further south the Tertiary beds attain possibly a thickness of from 3000 to 4000 feet.
