Ixiv PROCEEDINGS OE THE GEOLOGICAI SOCIETY. 



numbers ; at the same time the Lamellibranchiate MoUusca 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 con- 

 tinent 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 

 Kttoral 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 At- 

 lantic, 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 stiU. 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 evi- 

 dence 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 *. 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 move- 

 ments, 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. ' 



