Wallich^ on Siliceous Organisms. 
53 
are the forms which were observed by me in the Bay of 
Bengal and Indian Ocean^ floating near the surface in calm 
weather, in flocculent masses, from one to three inches long 
and that, although not seen floating in the same condition on 
the Atlantic side of Africa, I have repeatedly taken numbers 
of the larger Salpae, of six or seven inches in length, whose 
digestive sacs contained hardly any thing else. When swal- 
lowed by sea-birds, and freed from the nutritive material 
supplied by the bodies of the Salpae, these masses would 
naturally cohere in the manner described ; and it is highly 
probable, moreover, that the coherent tendency would be 
much increased by the partial conversion of a portion into 
soluble hydrates or silicates, the cementing property of which 
compounds is well known. 
This cohesive quality has been noticed also by the late 
Professor Bailey, of New York, as occurring in several 
diatomaceous deposits, but especially in that of California. 
Professor Bailey observes, " Some of these masses I endea- 
voured to break up by boiling in water and in acids, and also 
by repeated freezing and thawing when moistened, but with- 
out good results in either case. At last it occurred to me 
that the adherence might be due to a slight portion of a 
siliceous cement, which the cautious use of an alkaline solution 
might remove without destroying any but the most minute 
shell of the diatoms. As the case appeared a desperate one, 
a heroic remedy was applied, which was to boil small lumps 
of the diatomaceous mass in a strong solution of caustic 
potass or soda. This proved to be perfectly efiicacious, as the 
masses under this treatment rapidly split up along the planes 
of lamination, and then crumbled to mud.^^ f 
Now bearing in recollection this primary tendency of 
siliceous particles to cohere, let me review for a moment the 
conditions that present themselves to our notice. 
We find that the siliceous particles of the DiatomacecSj 
Polycystina, Acanthometr(B, and Sponges exist not only in a 
state of the utmost purity, but that they occur precisely in 
that state of minute subdivision which favours the solvent or 
aggregative process in an eminent degree. We see that they 
are gathered together by the Salpse, in the first instance, 
from the element in which they live, and that they are freed 
of all, or nearly all, their soft portions, by the action of the 
digestive cavities of these creatures. We find that the 
* 'Traus. Micros. Soc.,' vol. vi, p. 84. 
t 'American Journal of Arts and Sciences,' 2d Series, vol. xxi, May, 
1856. 
