REPOKT ON THE DEEP-SEA DEPOSITS. 
323 
north of the known limit of icebergs in this trip, still there were several frag- 
ments which appear to have been derived from icebergs : — 
Station 285, rounded fragments of granite, arkose ; 
,, 286, granite pebble ; 
,, 289, fragment of diabase ; 
,, 299, angular piece of granite ; 
,, 302, piece of granite coated with manganese, fragment of flint. 
If the positions of the fragments above enumerated be compared with a map showing 
the distribution of icebergs in the present seas, it will be observed that they are all 
within, or just beyond, the limits of the iceberg regions, and it cannot be regarded as 
other than a remarkable fact that the Challenger should not have found any fragments 
of continental rocks in the central portions of the ocean basins, except in the localities 
indicated. The position, then, in which these blocks and fragments of continental 
rocks were found is in itself sufficient evidence that they have been transported by 
floating icebergs and icefields of the present or of recent geological times. This view is 
confirmed by the nature and character of the transported material. The blocks are of 
all sizes, from several feet in diameter to the smallest dimensions ; their angles are 
sometimes rounded or softened, at other times sharp, and the larger fragments are 
frequently covered on one or more surfaces by glacial striations. In their nature the 
fragments are very heterogeneous, being derived from almost all the varieties of the rocks 
that crop out on the surface of the continents. This great variety in the dimensions and 
lithological nature of the continental debris spread over the floor of the ocean towards 
the polar regions of either hemisphere is exactly what we would expect to find in 
materials transported by floating ice. The glaciers, which give birth to the icebergs, in 
passing over the continental surfaces would necessarily carry away large and small frag- 
ments of all the continental rocks cropping out at the surface. The icebergs, in widely 
distributing these continental materials, would produce in the deep sea a deposit con- 
taining fragments of granite, gneiss, quartzite, schists, dolomites, crystalline limestones, 
and even fragments of volcanic rocks. The heterogeneity of such a deposit is thus in 
striking contrast, so far as its mineralogical constituents are concerned, to the homo- 
geneity presented by truly pelagic deposits, in which, as we have seen, volcanic materials 
alone make up the inorganic portion of the deposit. 
While icebergs are the only agents that are capable of effecting this wide distribution 
of continental rocks and minerals, Mr. Murray has shown that both seals and penguins 
carry to sea large numbers of stones and rounded pebbles in their stomachs, to which the 
sealers give the name of “ballast.”^ These animals may therefore, to some extent, dis- 
tribute rock fragments to great distances from the land. Should any of them be killed 
* See Zool. Chall. Exp., pt. viii. pp. 126, 127 ; also Turner, Report on the Seals, Zool. Chall. Exp., pt, Ixviii. p. 136. 
