DOCTRINE OP GEOLOGICAL CONTINUITY. 279 



Cretaceous period," and that the "ooze" now forming at great depths 

 in the North Atlantic is merely a continuation in time of the great 

 and well-known deposit of the white chalk. The points of resem- 

 blance by which this is sought to be established, are these : — 1. The 

 Atlantic "ooze" is a whitish or grayish-looking mud containing about 

 sixty per cent, of carbonate of lime, with from twenty to thirty per 

 cent, of silica, and a variable quantity of alumina. When dry, and 

 especially if consolidated, it would, therefore, approximate more or 

 less closely in mineral composition and texture to white chalk. 

 2. The abyssal mud of the Atlantic is to a very large extent com- 

 posed of the microscopic shells of Foraminifera, some of which are 

 specifically identical with cretaceous forms; whilst, as shown by Mr. 

 Lonsdale, the chalk is mainly composed of the debris of these minute 

 organisms. 3. The Atlantic " ooze " contains numerous siliceous 

 sponges, in many respects comparable with the sponges which are so 

 characteristic of the Cretaceous period. 4. The Atlantic "ooze" 

 contains numerous Echinoderms, epecially sea-urchins and Crinoids, 

 such as abounded in the chalk period ; whilst one of the latter is 

 referable to a Cretaceous type, hitherto believed to be extinct. 

 5. "We have reason to suppose that the conditions under which the 

 white chalk was formed, were very similar to those now present in 

 the Atlantic at great depths. 



On the other hand, as pointed out by Sir Charles Lyell and Mr. 

 Prestwich, the difference between the Atlantic ooze and the white 

 chalk are, to say the least of it, quite as numerous and as weighty as 

 the resemblances : — 1. The white chalk differs to an important extent 

 from the "ooze" in mineral composition; for it is composed of from at 

 least eighty up to as much as ninety nine per cent, of pure carbonate 

 of lime. 2. Little stress can be laid upon the occurrence of identical 

 species of Foraminifera in both deposits ; for it is well known that 

 such lowly-organized forms of life have an extraordinary power of 

 persistence, surviving geologieal revolutions which are fatal to higher 

 organisms. 3. The presence of some Cretaceous forms in the Atlantic 

 ooze is far more than counterbalanced by the total absence of all 

 those fossils which may be considered pre-eminently the fossils of the 

 Cretaceous period ; such as the various forms of Cephalopoda, especially 

 the Ammonitidae, and the Bivalve Molluscs. 



Mr. Prestwich, therefore, concludes that although it is probable 



