for any other limestone. Although hard in Central Europe it is almost as soft as in England when met with in Russia.

In the absence of positive knowledge as to the nature of deep sea mud Sir Charles Lyell and others, struck by the interesting observations of Mr. Darwin on coral reefs, and by some resemblances between chalk and the fine mud at the bottom of coral lagoons, had set men's minds thinking how far the coral animal and the fishes that feed on coral might be responsible for this variety of calcareous rock. Although the idea was plausible, further observation has shown that it is rather the Oolites than the chalk deposits that have been thus formed. Lagoons enclosed by coral receive beyond a doubt a vast quantity of fine mud that might represent chalk, but this is usually mixed with a far greater variety of fossils, especially of corals and bryozoa, and a more plentiful sprinkling of echinodermata, crustacea, and even shells than are at all usual in chalk.

It was not till the year 1858, when the British steamer Cyclops, commanded by Captain Dayman, following nearly in the course of exploration pursued by Lieutenant Berryman in the United States steamer Arctic, was systematically employed to take deep soundings and determine the nature of the sea bottom, that the real material at the bottom of deep water in the Atlantic was obtained and brought to the surface in quantity sufficient to permit of accurate observation. It was no easy or simple matter at first to lift even a small quantity of the scrapings of the sea bottom through 10,000 feet of water, but this has now become an ordinary and necessary result of every deep sounding.

It is no part of the object of the present article to repeat the accounts already frequently given of the methods by which deep soundings and dredgings in deep water have been accomplished. Various methods have been adopted, with various but gradually increasing success, until at last actual dredging has been carried on and nearly two hundredweight of the sea bottom, with its living inhabitants and the skeletons of the recently dead, has revealed a submarine life at a depth of more than 2,000 fathoms, not less varied nor less numerous, and certainly not less interesting, than that which may be studied within the few feet of tidal range near the shore. These results have been obtained in many parts of the North Atlantic, and year by year this ocean bed has been more and more the subject of investigation.

It may be well to remind the reader that between the land of Western Europe (including the British islands) and the east coast of North America (including Greenland), there is a space of nearly 1,500 miles of ocean, for the most part more than 1,000 fathoms deep, but imperfectly interrupted by banks. These banks rise into land in Iceland and the Faroe islands,

and probably approach near the water surface somewhere about latitude 55° N. and longitude 30° E., where according to old accounts there was once land. The telegraph plateau, as it is called the line of sea bottom on which the first Atlantic telegraph was successfully laid-lies a little to the south of this bank and is much deeper. To the north there is the Arctic Ocean covered most part of the year by ice, and only communicating occasionally with the Pacific Ocean by narrow choked up channels. To the south there is the Gulf Stream, a current of warm water, at the surface certainly approaching mid-Atlantic, whatever may be its extension towards the shores of Europe. Warm water is brought in this way across the Atlantic steadily, incessantly, and in large quantities, and it is quite impossible that the drag of this great stream-current should not even by mere friction produce a current of some depth. It is certain that in some places the warm current reaches the actual sea bottom.

Recent observations have shown that besides this warm current reaching the latitude of 50°, the part of the Atlantic canal we have alluded to above is affected by certain causes which produce real and well-defined currents, some near the surface, some near the bottom, some warmer than the mean temperature of the air above, and some cooler. There are broad and deep warm currents running from south-west to north-east, and other broad and deep cold currents running from north-east to south-west, and this complication of currents, influenced, there cannot be a doubt, by the form of the sea bottom, appears to have produced certain natural history results which are of the most extraordinary significance with reference to the geological question we are considering. It is in this respect, perhaps more than any other, that the value of recent observations concerning deep sea temperature must be measured.

That there is an important arctic drift running down along the coast of Greenland, conveying ice occasionally, and for some cause turned northward at the southern extremity of Greenland into Davis's Straits, has been long known. It is this current that renders Greenland almost uninhabitable, in latitudes where in Norway and Sweden we have a very pleasant climate and a large population. The cold or arctic current runs between the west coast of Iceland and the east coast of Greenland. (See Chart in Plate.) There are also powerful currents at a very low temperature proceeding through Hudson's Straits, entering the Atlantic near Newfoundland, and crossing the warm Gulf Stream.

One part of the great arctic current running along the east coast of Iceland passes down into the Atlantic to the south-west and is there soon lost. Another part, however, still further to

the east, runs between and past the Faroe islands and the bank called Rockall; while a third cold current passes along the coast of Scotland. All these are in comparatively shallow water, rarely exceeding 1,000 fathoms, and all are strictly limited by

natural barriers.

It is not to be supposed that there can be this continual drain of cold water from the arctic seas without some supply being drifted in by counter currents. No doubt there is a very large and constant evaporation from the mid-Atlantic, but there is also a heavy rainfall and a large number of streams pouring into the ocean the drainage both of Europe and America. There are in fact two deep warm currents, one between Iceland and the Rockall and Faroe banks, and the other between these banks and Scotland both also shut in by natural barriers.* These warm currents proceed from a deep central warm tract of ocean lying to the east and north-east of the limit of the Gulf Stream, and it is this warm tract, with its branches northwards, that affords in its floor the conditions apparently most favourable for certain deposits that have lately been described as resembling chalk.

The deep sea explorations of late years carried on with improved means of determining bottom temperature, have made it clear that there are well marked deep areas that possess a warm temperature, not very far from other areas where the bottom temperature is uniformly low. It is a further result of the same work that over the cold areas generally the bottom is sandy, often of volcanic sand, and these parts exhibit a considerable variety and sometimes a great wealth of animal life; but the organic forms but a small proportion in comparison to the inorganic element. Here, however, a vast multitude of the curious worm-like marine animals assuming a coat of agglutinated grains of sand have been met, and the multitude of new species obtained in recent soundings is so great that there is a difficulty in finding names for them. Besides annelids, sponges, echinoderms, mollusks, and crustaceans have been found, so that these regions are, on the whole, exceedingly rich. In one spot alone where the dredge brought up but little, a tangle of hemp lifted at one haul many thousand specimens of a single form of echinus.

On the other hand, in the warmer areas the deposit of mud consisted exclusively of a peculiar material called ooze or oaze

It was found in the recent (1869) expedition that a difference in bottom temperature, between 32° and 47°, existed at points only eight or ten miles distant beneath a uniform surface temperature of about 52°. In such cases the cold area was paved with barren sandstone having a scanty boreal fauna, while in the adjacent warm area the bottom was mud, with an abundant temperate fauna.

by nautical people-a soft mealy substance, having the appearance of mud but of very close texture. This substance is described as remarkably sticky, having been found to adhere to the sounding rod and line through its passage from the bottom to the surface, in some instances more than 2,000 fathoms. When a little of this mud is taken out and thoroughly dried it becomes white or reddish-white and (though less white) it closely resembles very fine chalk.* Fully nine-tenths by weight of this deposit was estimated by Professor Huxley to consist of minute skeletons of Foraminifera, composed of carbonate of lime. Examined under the microscope it presents a vast multitude of exceedingly minute granules and fragments, and a certain proportion of some clear mineral, perhaps quartz, perhaps volcanic sand. The granules and fragments are almost without exception referable to one species of Foraminifera known as Globigerina, traced through a complete series of gradations from less than one-thousandth of an inch in diameter (when it consists of one or two cells) to more than one-sixtieth of an inch. The general appearance of the complex forms consisting of several cells is given in the plate annexed. Among the mud that does not consist of fragments of Globigerinæ are fragments of diatoms and indications of sponges. When these remains were first found to form a large part of the mud in depths of upwards of 2,000 fathoms, and it became clear that they were uniformly spread over a large space, the knowledge of the existence of animal life in deep water was so small that many naturalists speculated as to the possibility that the accumulation consisted only of the skeletons-the animals themselves having lived near the surface. Subsequent observations have shown that there is no known limit of depth at which animal life ceases. There can hardly be a doubt that the Globigerinæ are the natural inhabitants of the ocean floor at all depths under favourable conditions, and that these conditions consist of a warm, or comparatively warm, sea bottom. It is also certain that a warm sea bottom is a local condition nearly independent of latitude-absent in some seas whose surface water is very warm, and present in others where the surface and moderate depths are very cold.

In the dredging expedition of 1868, a large quantity of Globigerina mud was lifted always from the deep warm bottoms; but this mud was found to include animal life of higher types and was everywhere permeated by a peculiar glairy organic substance, regarded by Prof. Huxley as an intermediate condition between plant and animal life, and called by him Bathybius. The nature and true position of this remarkable substance is not

Huxley's Appendix to Capt. Dayman's account of Deep-Sea Soundings in H.M.S. Cyclops.

yet satisfactorily made out, but the bottom temperature that appears most favourable to the rapid multiplication of these organisms would seem to be about 45°, and the depth of water at least 2,000 fathoms.

It is worthy of notice in reference to this, as in other matters connected with deep sea dredging, that the first suggestions and the germ of much of the theory that has been lately advocated by the distinguished naturalists who were selected by the Council of the Royal Society to conduct the enquiry for which sounding and dredging ships have been granted by Government, was due to Dr. Wallich, who accompanied Captain McClintock in the Bulldog, and the results of whose observations were published in various ways between 1860 and 1862. In the year 1860, after his return from the Bulldog expedition, Dr. Wallich pointed out the absolute confirmation of previous observations as to the presence of animal life at great depths, which were till then doubtful owing to the absence of certainty as to actual depth, and a belief that the remains found might have sunk from the surface. That the minute foraminifera, and even other larger and more complex forms of life, dwelt in deep bottoms was proved by the bringing up of a living starfish from 2,000 fathoms, and perhaps yet more conclusively by examining the contents of the stomachs of the animals coming from the bottom and only recently dead. Dr. Wallich, in his account of the natural history results of the Bulldog expedition, called attention to all these facts, suggesting their importance as pointing to the possible origin of chalk, distinctly advocating the view that there may exist in these deeper parts of the sea an intermediate form of protoplasmic life neither animal nor plant, but common to both, and urging strongly the necessity of further exploration. Dr. Wallich afterwards endeavoured through the Council of the Geographical Society, to induce the Government to place a ship at the disposal of qualified naturalists for the prosecution of these researches, and employed the same arguments as those which were afterwards, and more successfully, used by the Council of the Royal Society with the same object. It is a matter of regret that the valuable services of Dr. Wallich in this matter have been grudgingly admitted in the published reports of the Royal Society Committee, and that Dr. Wallich himself has not received from the Society that recognition which his anticipation of their movement in the matter certainly deserved.

There are two or three things to be explained in reference to the origin of chalk, and among them the occasional bands of flint are perhaps among the most important. As white chalk is nearly pure carbonate of lime, so flint is generally almost pure silica. The flint is present in occasional lumps of strange