111 
division appears to continue indefinitely, so that we may have 
resulting a great number of single and separate individuals, 
or a chain of united individuals from a single one. Under 
either circumstances the rate of increase in number is ex- 
tremely rapid, as can be readily understood if we imagine, for 
instance, that the subdivision of the first single cell into two, 
occupied the space of time of fifteen minutes, which certainly 
is not too rapid for some of the Diatomacez. Then in the 
next fifteen minutes four individuals will have been formed ; 
in the next eight; in the next sixteen, so that at the end of 
twenty-four hours the number formed would amount to 
3,388,608 and a large space of water would in this way, have 
been peopled from a single individual Diatom. But whilst 
subdivision, or true growth, has been thus progressing, increase 
by generation or seeding may have taken place at the same 
time, and from each individual in turn, several young may 
have been brought forth, which would multiply the rate of 
increase very materially, of course. It is true that the mode 
of seeding of these organisms is not thoroughly understood, 
but we know enough to say that it does occur, and very fre- 
quently, and that the number of new individuals thus formed, 
is very great. At the same time numerous individuals are 
dlying, and as they do so much of the organic matter of 
which they are composed is dissipated, but some of it, along 
with the hard siliceous valves and connecting membranes 
which constituted the skeletons of the Diatoms, fall to the 
bottom of the pond, and form a layer of greater or less thick- 
ness, according to the time during which it has been accu- 
mulating. If it be exposed now by draining such a pond, 
it may appear as a brown or grey powdery mass, but if it has 
rested beneath the water sufficiently long, almost all of the 
organic matter will be removed, and the clean white siliceous 
skeletons alone remain. 
Such are the results, then, of this rapid growth of the 
Diatomaceze in ponds, lakes, marshes and rivers, and as the 
first examples of such deposits which I examined were found 
beneath layers of Peat, I gave to them the name “Sub-Peat”’ 
Deposits, and under that designation they have been generally 
. 
