DREDGING ON THE COASTS OF SHETLAND. 77 
pretty shell, and the stock seems to be inexhaustible. ‘Mr. Norman reminds me 
of Pomatoceros arietinus, Caryophyllia clavus, Comatula Sars, and Echinus 
Norvegicus as occurring under similar conditions. I am confident that if my 
distinguished friend were now alive, he would candidly acknowledge that 
his first impression had not been confirmed, or at least that it was modified 
by subsequent observations. 
No species appears to be confined to any limited district, although it may 
be locally distributed. The circumstance of its not having been found else- 
where is by no means a satisfactory proof that it does not exist beyond the sup- 
posed boundary. The more the bottom of the sea is explored, the greater 
will be the known extent of distribution. Instances in support of this pro- 
position are so numerous that it is hardly necessary to adduce them, Among 
the bivalves, Lepton squamosum, and among the univalves, Rissow abyssicola, 
may be cited as examples. Both of them were at one time said to be pecu- 
liar to our seas ; but it has now been ascertained that they have a wide range, 
north as well as south of Great Britain, in other parts of the Atlantic 
Ocean. 
The sea-bed is often greatly diversified within the same district, both as regards 
its shape and composition. Whenever the vessel was of sufficient size, I have 
had two dredges put out at the same time ; so that directly one has been taken 
up the other is being hauled in. It has more than once happened that the 
contents of the second dredge were quite different from those of the first, the 
one consisting of shell-sand and the other of stones, or vice versd. The 
depth of water remained the same. This change of ground must have taken 
place in the interval of a few minutes, when the first dredge was being 
taken up, and during which the vessel could not have drifted more than a 
couple of hundred yards. The vessel’s head is always kept nearly to 
windward while she is dredging, so that she may not have too much way. 
A mile an hour is reckoned quite fast enough to keep her steadily at work. 
Vast numbers of Gilobigerine abound everywhere in the dredged shell- 
sand. Dr. Wallich says*, “ It is evident that there is an intimate associa- 
tion between the Gilobigerina-deposits and the Gulf-stream ; for wherever 
we trace the one sweeping across the surface of the ocean, we are almost sure 
to detect the other resting on the sea-bed; and when we fail to trace the, 
one, we almost as surely fail to detect the other.” But it does not appear 
that the Gulf-stream impinges on the northern or eastern coasts of Shetland. 
No seeds, no Janthine, Velelle, or driftwood from the tropics have ever 
been picked up on these shores. On the contrary, the only driftwood 
which is here found floating or cast ashore consists of pine-trees from Nor- 
way—sometimes with their roots, and usually drilled by Teredo nana, being 
the same species that attacks fixed and submerged wood or boats lying long at 
anchor on the Shetland and Scandinavian coasts. Wood is too scarce and 
valuable a commodity in the treeless isles of Shetland to be disregarded by 
the natives. A Norway log is one of their chief prizes. It would seem 
from the foregoing facts that the Globigerina-deposits are generally distri- 
buted over the floor of the deep sea throughout a very extensive tract, irre- 
spective of the course of the Gulf-stream. 
Occasionally a little world of living animals is seen to occupy a single 
dead shell. An instance of such a microcosm was observed on a specimen 
of Buccinopsis Dalei, var. eburnea. Far within the shell an Annelid took up 
its abode. This may have been the first occupant after the true inhabitant 
had been cleared out, and it probably assisted in the evacuation. A Hermit 
* The North Atlantic Sea-bed, p. 137. 
