120 
POPULAR SCIENCE REVIEW. 
organic acids. That it did not assume the solid state until at 
least after the partial consolidation of the Chalk is obvious, 
through the filling in of fissures at right angles to the bedding, 
which could not have existed when it formed the surface sedi- 
ment of the ocean bottom. In comparing the White Chalk 
analysis with that of the ooze, therefore, we must hear in mind 
that, as already pointed out by Mr. Sorby, Mr. Sollas, and Dr. 
Wallich, a portion of flint must be added equal to that which 
has been separated away. In a similar manner, iron has been 
removed and segregated together, to be crystallized principally 
into globular balls with a radiating structure.* 
The shells composed of carbonate of lime, such as those of 
Gastropods,-)- Cephalopods, and Dimyaria, seem also to have been 
dissolved away, perhaps by the rain-water which falls upon the 
Chalk, saturates it, and passes through it by capillary action 
unceasingly- Another evidence of change is shown in the crys- 
talline condition of shells composed of phosphate of lime, such as 
the Aviculidse, the Branchiopoda, the Echinodermata, &c. 
It is surprising to find that no allusion whatever is made to 
this range of facts by Mr. Wallace ; and those of his readers who 
are unacquainted with them, are left unaware that Chalk has 
undergone such great changes in its composition since it was 
the bed of the sea, as to deprive the unqualified statement that 
the analyses of Chalk and Globigerina ooze ‘ do not even approxi- 
mately agree/ of any scientific value. 
These facts further tend to show, as indeed is obvious 
from a comparison of the faunas, that the similarity in the 
analysis of the Oahu chalk and the White Chalk, upon which so 
much stress is laid, is purely superficial.! In spite of the fact 
* It aBsumes very beautiful forms in the Grey Chalk, and has occasionally 
completely replaced Sponges. The iron is frequently ochreous in theWhite Chalk. 
t Gastropods are found as casts in the Grey Chalk, slightly coated with 
iron, and occasionally traces are met in the Lower White Chalk in the same 
condition. Higher than this even the most indistinct outlines of the larger 
forms, such as Fleur otomaria, are rare. I have seen but one trace of shell 
on any spiral Gastropod, and this on a fragment of Funis from the White 
Chalk near Norwich. Small thin fragments adhered to the cast, and the 
circumstance is remarkable as Funis almost alone of the Gastropods pre- 
serves its shell in the Cambridge Greensand. The shells of Cephalopods 
seem to possess a slightly greater resisting power, and their casts are, as a 
rule, more distinct. 
f Analysis of Oahu chalk : — 
Carbonate of Lime . 
92-800 
Carbonate of Magnesia . 
2-385 
Alumina .... 
0-250 
Oxide of Iron .... 
0-543 
Silica 
0-750 
Phosphoric Acid and Fluorine 
2113 
Water and loss 
1-148 
Geology of the U. S. Exploring Expedition , p. 150. 
