appear to be in such large numbers on the surface over the Diatom ooze as
they were a little further north. This may perhaps be accounted for by
our not having struck their belt of depth with the tow-net; or it is
possible that when we found it on the 11th of February the bottom deposit
was really shifted a little to the south by the warm current, the
excessively fine flocculent _débris_ of the Diatoms taking a certain time
to sink. The belt of Diatom ooze is certainly a little further to the
southward in long. 83° E., in the path of the reflux of the Agulhas
current, than in long. 108° E.

"All along the edge of the ice-pack--everywhere, in fact, to the south of
the two stations--on the 11th of February on our southward voyage, and on
the 3rd of March on our return, we brought up fine sand and grayish mud,
with small pebbles of quartz and felspar, and small fragments of mica-
slate, chlorite-slate, clay-slate, gneiss, and granite. This deposit, I
have no doubt, was derived from the surface like the others, but in this
case by the melting of icebergs and the precipitation of foreign matter
contained in the ice.

"We never saw any trace of gravel or sand, or any material necessarily
derived from land, on an iceberg. Several showed vertical or irregular
fissures filled with discoloured ice or snow; but, when looked at
closely, the discoloration proved usually to be very slight, and the
effect at a distance was usually due to the foreign material filling the
fissure reflecting light less perfectly than the general surface of the
berg. I conceive that the upper surface of one of these great tabular
southern icebergs, including by far the greater part of its bulk, and
culminating in the portion exposed above the surface of the sea, was
formed by the piling up of successive layers of snow during the period,
amounting perhaps to several centuries, during which the ice-cap was