HISTOEY OF THE CREIACEOUS FLINTS. 79 



those used by Sir Charles Lyell, which were cited in an earlier part 

 of these observations. It is, I trust, needless for me to say that in 

 venturing to contest any opinion emanating from so illustrious a 

 source, I do so with the greatest reluctance, and only under a con- 

 viction that his conclusions, however justified by the data which 

 were at his command in relation to the profusion of the Diatomaceae 

 in the Atlantic, and the predominating share taken by these or- 

 ganisms in the formation of the flints, were vitiated in consequence 

 of the data being erroneous. Por, I repeat (and without fear of 

 contradiction) that in the IN'orth Atlantic, to which Sir Charles 

 Lyell's remarks applied more particularly, there never has been met 

 with a true calcareous mud in which the percentage of Diatom- 

 remains is so great as to deserve mention in connexion with the 

 flint-formation. Neither is there any authentic evidence forth- 

 coming to show that Diatomaceous deposits have in time past ex- 

 isted, at depths such as that indicated (2400 feet), along the North- 

 Atlantic coast-lines, of sufficient importance to deserve mention. 

 Where they occur they are of Posttertiary origin, and have been 

 formed in freshwater bottoms. Should this be granted, there is the 

 clearest warrant for assuming that the comparatively bulky siliceous 

 framework and spicule-system of the deep-sea vitreous sponges must 

 constitute the main source of supply of that material for the flints. 

 Indeed it is far from improbable that the true flints are produced 

 solely in the areas occupied by the sponge-beds, the flints becoming 

 more cherty and devoid of those characteristic amoebiform outlines 

 which, according to my hypothesis, are dependent on the presence 

 of, and the combination of the silica with, the accumulation of 

 nearly pure protoplasm stiU sufficiently recent to have resisted ad- 

 mixture with calcareous or other matter. 



But it is not only necessary that an adequate supply of fresh and 

 free protoplasm should be present at the sea-bed, but that proto- 

 plasm, not of necessity pure and homogeneous, should be present in a 

 continuous flocculent layer overlying the calcareous deposit. Now 

 this is precisely the condition in which the subsidiary portion exists 

 which is not derived from the sponges, but from the Poraminifera. 

 This very remarkable condition, of the full significance of which I 

 was not aware till the history of the deep-sea sponges was revealed 

 some ten years ago by Dr. Carpenter and Sir Wyville Thomson, was 

 first pointed out by me in 1860 as occurring over the Globigerine 

 areas of the North Atlantic ; and it has since then been completely 

 verified by the above-named observers. As it furnishes the key to 

 the entire process of flint-formation, 1 may be permitted to cite the 

 description given of it in part 1 of my ' North-Atlantic Sea-bed,' 

 pubHshed in 1862. 



" The flocculent character is distinctly observable on the imme- 

 diate surface-layer of all the deposits, and in a few cases, in which 

 the quantity of extremely fine amorphous particles is excessive, it 

 extends to some depth. Such is the condition where the Porami- 

 nifera are either absent or constitute the smallest percentage of the 

 material. 13 at, in the majority of the deposits, tlie ilocculcncc docs 



