Sea-bottom procured by H.M.S8. ‘Challenger.’ 295 
a like replacement is going on at the present time, the chambers 
of recent Foraminifera being occasionally found to be occupied by 
nineral deposit, which, when the shell has been dissolved away 
by dilute acid, presents a perfect internal cast of its cavities. By 
the application of this method to Mr. Beete Jukes’s Australian 
dredgings, my coadjutors, Messrs. W. K. Parker and T. Rupert 
Jones, obtained a series of internal casts of most wonderful beauty 
and completeness, on which I have based my interpretation of the 
organic structure of Hozoon canadense. Having myself examined 
in the same manner a portion of the Foraminiteral sand dredged 
by Capt. Spratt in the AXgean (kindly placed in my hands by Mr. 
J. Gwyn Jeffreys), 1 have found that it yielded a great variety of 
these beautiful models, not only of the bodies of Foraminifera, but 
also of the sarcodic network which interpenetrates the calcareous 
network of the shell and spines of Echinida*. 
Alike in Mr. Jukes’s and in Capt. Spratt’s dredgings, some of 
these casts are in green silicates and some in ochreous, corresponding 
precisely to the two kinds of fossil casts described by Prof. Ehren- 
berg. The difference I presume to depend upon the degree of 
oxidation of the iron; but as these casts are far too precious to be 
sacrificed for chemical analysis, 1 cannot speak with certainty on 
this point. 
As it is only in certain limited areas of the sea-bottom that this 
replacement of the sarcodic bodies of Foraminifera by mineral 
deposit is met with, it has always seemed to me next to certain 
that there must be some peculiarity in the composition of the sea- 
water of those areas (produced, perhaps, by the outburst of sub- 
marine springs highly charged with ferruginous silicates) which 
gives to them a capability that does not exert itself elsewhere ; 
and this now seems yet more probable from the circumstance that, 
notwithstanding the vast extent over which the ‘ Challenger’ 
soundings and dredgings have been prosecuted, only two or three 
cases of the kind have been noted—those, namely, of the “ green- 
ish sands” brought up from 98 and 150 fathoms in the region 
of the Agulhas Current and in one or two other localities. 1t is 
a fact of peculiar interest, moreover, that the calcareous shells 
should have here disappeared, just as they have done in ordinary 
green-sand—and this, too, although the depth was so small as 
altogether to torbid the idea that their disappearance is due to any 
solvent process brought about by the agencies to which Prof. 
Wyville thomson attributes the removal of the calcareous deposit 
generated by Globigerine life. 
Now, in the residue left after the decalcification of Capt. Spratt’s 
dredgings, I noticed a number of small particles of red clay, some 
of them presenting no definite shape, whilst others approximated 
sulliciently closely in form and size to the green and ochreous 
* Of these I hope to be able, ere long, to give a detailed account, in illus- 
tration of the similar models of the animal of Hozoon obtained by the decalci- 
fication of its serpentine lamellix, 
