these may be added various irregular forms, long flexuous lobes packed side by side, or chrysalis-like forms with two or three longitudinal series of chambers packed closely like wedges, some regularly and others irregularly. In fact, there is such a multiplicity of forms (figs. 5,6,7,8,9) that they might be called polymorphous, and even a single species, as now understood, may include individuals which diverge remarkably from each other. It would be almost an exaggeration to say that no two individuals are exactly alike, but one is almost tempted to think so, in presence of such a multiplicity of form.

FIG. 7.-ENTOMOSTEGA.

One important result of deep-sea dredging has been to exhibit the relationship of the floor of the sea to the chalk deposit of the "dear white cliffs of Dover." "The dredging at 2,435 fathoms at the mouth of the Bay of Biscay," writes Sir Wyville Thomson, “gave a very fair idea of the condition of the bottom of the sea over an enormous area, as we know from many observations which have now been made with the various sounding instruments contrived to bring up a sample of the bottom. On that occasion the dredge brought up about cwt. of calcareous mud. There could be little doubt, from the appearance of the contents of the dredge, that the heavy dredge frame had gone down with a plunge, and partly buried itself in the soft, yielding bottom. The throat of the dredge thus became partly choked, and the free entrance of the organisms on the sea floor had been thus prevented. The matter contained in the dredge consisted mainly of a

FIG. 8. ENALLOSTEGA.

compact "mortar," of a bluish colour, passing into a thin-evidently superficial-layer, much softer and more creamy in consistence, and of a yellowish colour. Under the

microscope the surface layer was found to consist chiefly of entire shells of Foraminifera (Globigerina bulloides), large and small, and frag

IG. 9. STICHOSTEGA.

ments of such shells mixed with a quantity of amorphous calcareous matter in fine particles, a little fine sand, and many spicules, portions of spicules, and shells of Radiolaria, a few spicules of sponges, and a few frustules of diatoms. Below the surface-layer the sediment becomes gradually more compact, and a

E

slight grey colour, due, probably, to the decomposing organic matter, becomes more pronounced, while perfect shells of Globigerina almost entirely disappear, fragments become smaller, and calcareous mud, structureless and in a fine state of division, is in greatly preponderating proportion. One can have no doubt, on examining this sediment, that it is formed in the main by the accumulation and disintegration of the shells of Globigerina; the shells fresh, whole, and living, in the surface layer of the deposit, and in the lower layers dead, and gradually crumbling down by the decomposition of their organic cement, and by the pressure of the layers above; an animal formation, in fact, being formed very much in the same way as in the accumulation of vegetable matter in a peat-bog; by life and growth above, and death, retarded decomposition, and compression beneath." 1

The foregoing extract, for which reason we have given it in full, shows some points of remarkable similarity between the Atlantic ooze and deposited chalk. There may be differences in chemical composition, but, when submitted to microscopical examination the resemblances are so great, or, as Sir Wyville Thomson says, "sufficiently striking to place it beyond a doubt that the chalk of the cretaceous period and the chalk mud of the Atlantic are substantially the same." "Altogether, two slides, one of washed-down white chalk, and the other of Atlantic ooze, resemble one another so nearly that

it is not always easy for even an accomplished microscopist to distinguish them."

In order to remove all doubt as to the impression he intended to convey, the same writer emphasises this point subsequently, when he writes :--" There

can be no doubt, whatever, that we have, forming at the bottom of the present ocean, a vast sheet of rock which very closely resembles chalk, and there can be as little doubt that the old chalk, the cretaceous formation which, in some parts of England, has been subjected to enormous denudation, and which is overlaid by the beds of the tertiary series, was produced in the same manner, and under closely similar circumstances; and not the chalk only, but, most probably, all the great limestone formations. In almost all of these the remains of Foraminifera are abundant, some of them, apparently, specifically identical with living forms."1 It was under these impressions, and with these views, that he publicly used the expression to which geologists took exception, that "we might be regarded, in a certain sense, as still living in the cretaceous period." But it seems that the mode of expression was censured rather than the opinion, since he afterwards declared that "the doctrine of the continuity of the chalk, in the sense in which we understood it, is now very generally accepted." In confirmation of this view may be cited the remarks of Professor Huxley, in his anniversary address as President of the Geological Society, in 1870, when he said, "Many years ago I ventured to speak of the Atlantic mud as 'modern chalk,' and I