THE PERMANENCE OF CONTINENTS. 
119 
A new species of C ary ophy Ilia, allied by its structural pecu- 
liarities to C. Bowerbanki of the Gault, and a species identical 
witb tbe well-known Cary ophy Ilia cylindracea, Reuss, sp., were 
discovered at the same time. The homotaxis of part of the 
Coral fauna of the Atlantic and that of the Cretaceous ocean, 
Prof. Duncan considers to be very remarkable. 
Against this well-nigh irresistible evidence in favour of the 
oceanic origin of Chalk, Mr. Wallace states that no specimen of 
Globigerina ooze yet examined agrees, even approximately, with 
Chalk in chemical composition. The differences between the few 
analyses that have been published, are chiefly in the relative 
quantities of carbonate of lime, silica, alumina, and oxide of iron. 
It is by no means apparent that Sir W. Thomson’s sample is 
the nearest analogous deposit to Chalk that could be found in 
the beds of the Atlantic or Pacific ; but supposing it to be so, 
the great changes in chemical composition to which Chalk has 
been subjected since its consolidation, are entirely overlooked 
in comparing the analyses.* Chalk is, and probably always has 
been since its upheaval, constantly saturated with percolating 
rain-water, which enters as soft water charged with carbonic 
acid, and comes out in springs of hard water charged with car- 
bonate of lime ; and this alone in the course of ages would 
carry away the more soluble constituents such as iron, alumina, 
and magnesia. An even more important change is due to the 
removal by segregation of its silica into the form of flint. This, 
doubtless, took place when the silica was in a colloid state, and 
seems to have been arrested, whilst the Chalk was consolidating, 
wherever harder and softer layers alternate. Its once viscid, 
almost fluid, state is shown by the manner in which it has pene- 
trated the minutest pores of Echinoderms before destroying the 
shell ; and it seems probable from the way in which it has re- 
placed carbonate of lime, "I* that it had not parted with its 
* The analyses relied upon in support of this are by Sir W. Thomson, of 
Globigerina ooze, viz. : — 
Carbonate of Lime 
Carbonate of Magnesia . 
Alumina and Oxide of Iron 
Silica 
Supposed Volcanic Dust 
And of Chalk, by David Forbes 
Carbonate of Lime 
Carbonate of Magnesia 
Alumina and Phosphoric Acid 
Chloride of Sodium . 
Insoluble debris 
43*93 to 
79-17 per cent. 
1-40 to 
2-58 
6-00 P to 
32-98 „ 
4*60 to 
11-33 „ 
4-60 to 
8-33 „ 
Grey Chalk, 
White Chalk, 
Folkestone. 
Shoreham. 
94-09 
98-40 
0-31 
0-08 
a trace 
0-42 
1-29 
— 
3-61 
1-10 
t All the carbonate-of-lime shells are replaced in the Blackdown deposits 
by silica. 
