CHAP. X.] CONTINUITY OF THE CHALK. 477 



The wide extent of Tertiaries in Europe and the 

 north of Africa sufficiently proves that much dry land 

 has been gained in tertiary and post-tertiary times, 

 and the great mountain-masses of Southern Europe 

 give evidence of great local disturbance. But al- 

 though the Alps and the Pyrenees are of sufficient 

 magnitude to make a deep impression upon the 

 senses of men, taking them together, these moun- 

 tains would if spread out only cover the surface 

 of the North Atlantic to the depth of six feet, and 

 it would take at least two thousand times as much 

 to iill up its bed. It would seem by no means im- 

 probable, that while the edges of what we call the 

 great Atlantic depression have been gradually raised, 

 the central portion may have acquired an equivalent 

 increase in depth ; but it seems most unlikely that 

 while the main features of the contour of the northern 

 hemisphere remain the same, an area of so vast extent 

 should have been depressed by more than the height 

 of Mont Blanc. On these physical grounds alone we 

 are inclined to believe that a considerable portion of 

 this area has been continually under water, and that 

 consequently a deposit has been forming there unin- 

 terruptedly, from the period of the chalk to our own. 

 I will now turn to the palseontological bearings of 

 the question. Long ago Mr. Lonsdale showed that 

 the white chalk was mainly made up of the debris of 

 foraminifera, and Dr. Mantell estimates the number of 

 these shells at more than a million to a cubic inch. 

 In 1848 Dr. Mantell, speaking of the chalk, says 

 that it "forms such an assemblage of sedimentary 

 deposits as would probably be presented to observa- 

 tion if a mass of the bed of the Atlantic, 2,000 feet 



