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which not unfrequently attain a thickness of thousands of feet, and cover areas measured by thousands of square miles, must all, with very few exceptions, have been formed by the agency of plants and animals.

Silica is present in sea-water in much smaller proportions than carbonate of lime. It is, indeed, difficult to obtain any estimate of the proportions in which natural waters contain this substance. Certain investigations of Forchammer point to the conclusion, however, that silica is never present in sea-water to the extent of 1 part in 50,000, and that probably 1 part in 100,000 would be a very liberal estimate indeed. Nevertheless, those minute plants the diatomacea, with the animals known as radiolarians, and siliceous sponges, extract the minute proportion of silica from sea-water to build up their exquisitely beautiful skeletons; and these, on the death of the organisms, accumulate to form great masses of siliceous rock.

Phosphate of lime is probably not present in greater quantity in sea-water than silica, yet the bones of fishes and the shells of crustacea and other organisms are largely composed of this substance; and, as is shown in the interesting Challenger volume to which we have referred, very important de posits of this substance are being formed on many parts of the ocean-floor.

Salts of iron, though present in seawater, must exist in very minute quantities. The same is true with respect to the waters of rivers and lakes; yet compounds of this metal are extracted from their state of solution in water by various organisms, in the remains of which they may easily be detected by analysis. In the case of the pisolitic ores found on the beds of the Swedish lakes, we have an example of what can be done in separating salts of iron from a state of solution by a very lowly organized plant, "Didymohelix" (the Gallionella ferruginea of Ehrenberg). The crop of iron-ore, if removed from the bed of the lake by dredging, is renewed in the course of a few years by the growth and multiplication of these plants.

In the same way, all the elements which occur in the ashes of marine plants and animals-and a very large

number of the elements have been detected in these ashes-must have been extracted, in some form of combination, from sea-water; being taken by the organism either directly from the medium in which it lives, or indirectly in the food passed through its body.

Recent observations of very great interest have shown that, even in those cases where carbonate of lime seems to be separated from water by purely chemical agency, living and growing plants really play an important part in the process. In the formation of those masses of calcareous rock known as travertine, which are left behind when springs of water highly charged with carbonate of lime flow out at the surface, the cause of the deposition has usually been held to be the evaporation of the water and the escape into the air of free carbonic acid from it. But the eminent German botanist, Professor Ferdinand Cohn, has shown that the really efficient agents in removing the free carbonic acid, which holds the mineral matter in solution, are numerous minute and lowly plants, and that around these plants the solid matter is deposited, as the water is rendered incapable of longer holding it in solution by the action of the living organisms. A very curious fact pointed out by this observer is that these minute plants are active agents in the formation of the pisolitic deposit of Carlsbad (the Sprudelstein), and that the organisms which in this case perform such an important work are capable of living at a very high temperature; they flourish, in fact, in waters only a few degrees below the boiling point.

It is a well-known fact that the waters of the hot springs of the Yellowstone National Park in North America, and the siliceous and calcareous materials deposited by them, owe their brilliant and varied colors to the numerous forms of plant-life that multiply and grow in the waters, even when at very high temperatures. Whether the deposition of silica, as well as of calcareous matter, is in any way aided by the action of these growing plants-as has been maintained by certain American observersis a point on which some difference of opinion still exists.

The mention of the pisolitic masses of Carlsbad cannot fail to suggest to the

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geologist the question of the origin of those widely distributed limestones known as "oolites" or "roe-stones, which are found in all the formations of the earth's crust, from the oldest to the youngest. Many years ago Sir Henry De la Beche pointed out that very similar rounded grains to those composing our Portland, Bath and Ketton limestones are being formed at the present day, on tropical shores, especially around coral-reefs, and his observations have been confirmed by Nelson and other investigators. Sorby, by a study with the microscope of thin sections of the recent grains and their analogues of former geological periods, has demonstrated their substantial identity. All the early observers seem to have concluded that in the shallow pools and lagoons about coral-reefs an actual deposition of calcareous matter must be going on, owing to the evaporation of the sea-water, and the escape from it of free carbonic acid; and that, in consequence of this concentration, minute shells and other objects become centres around which successive layers of carbonate of lime are deposited. But very careful microscopical study of preparations of the modern and ancient oolite grains reveals the fact that they exhibit traces of curious folded and branching tubes, and there is the strongest ground for believing, that as in the structures so well described by Cohn, the deposition of carbonate of lime is aided, and perhaps entirely effected, by the agency of minute vegetable organisms. Mr. E. Wethered has indeed shown that, in the limestones of all ages those obscure organisms, consisting of twisted and sometimes branching tubes -which have received the names of Girvanella, Micheldeania, etc. are very abundant, often making up large portions of the calcareous mass; and that these organisms are plants which have the power of secreting calcareous matter within their cell-walls or of causing it to be deposited outside them, is now maintained by botanists of wide experience and knowledge. It can scarcely be doubted that in salt-water no less than in fresh-water the growth of plants taking up carbonic acid leads to the deposition, within or outside their tissues, of calcareous material

that may accumulate to form great rock

masses.

It is very interesting to note that while certain plants are thus engaged in building up limestone rocks by investing minute shells and shell-fragments with successive layers of calcareous material, other organisms of the same class are occupied in a work having an exactly opposite tendency, namely, that of boring into and dissolving away the substance of calcareous organisms. The late Professor P. M. Duncan called attention to the fact that fossil corals and other organisms are frequently found to be perforated by fine tubes, and his conclusion that these tubes were produced by a parasitical vegetable organism, which in its growth dissolves away and thus penetrates into calcareous skeletons, was confirmed by several observers. More recently the able French algologist, Ed. Bornet, has shown how abundant are organisms possessed of this remarkable power, and how widespread and striking are the proofs of their activity. It is difficult to find a fragment of shell, coral, or bone, either in the accumulation now taking place on the ocean-floor or in those which have been formed during earlier periods of the earth's history, that is not riddled in all directions by these curious perforations; and in many cases the calcareous masses have their whole substance so completely eaten away in all directions that they crumble to powder at the slightest touch. It is obvious, therefore, that these plants must play the part of scavengers, penetrating into and dissolving away the fragments of shells and other calcareous organisms on the ocean floor, and thus leading to their complete disintegration and removal. Bornet has not only described a number of genera and species of these burrowing plants, differing from one another greatly in the forms and characters of the tubes which they excavate, but he has performed a task of much greater interest and importance in working out the life-history, habits, and modes of reproduction of these singular and hitherto unknown members of the vegetable kingdom.

Among the most interesting of the problems brought into prominence by the researches carried on during the Challenger and other deep-sea exploring

expeditions is that of the origin of deposits of iron and manganese among the materials found upon the ocean-floor. Most of the muds upon all but the most profound portions of the ocean bed are characterized by a deep blue color, and the analyses of Mr. Buchanan have shown that this blue color is due to finely divided iron disulphide (iron pyrites). The surface layer of such muds may have a brown tint from the oxidation of the iron, but the deep blue tint is almost always found below the superficial brown layer. The same color, as is well known, prevails in most of the argillaceous, and in many of the calcareous and arenaceous deposits of the earth's crust; and the blue color of such masses of clay as constitute the Lias, the Oxfordian, the Kimeridge, the Gault, and the London-clay formations have long ago been shown by Ebelman and Church to be due to the dissemination through their mass of iron-pyrites in a very finely divided state.

It has been shown by Mr. Buchanan that the formation of the iron disulphide in the blue mud of the ocean-floor, is due to the action of the innumerable marine worms that pass the fine mud through their bodies, and throw it out in the form of worm-casts. Within the bodies of the worms, chemical action is continually going on, sulphur being separated from the sulphates dissolved in the sea-water to form sulphuretted hydrogen, while iron, extracted from the water by the breaking-up of the carbonate, unites with it to form the iron disulphide. The foul smell of these muds when they are first brought to the surface in the dredge affords evidence of the chemical action going on in them. Mr. Buchanan has justly dwelt upon the similarity of the operations taking place upon the ocean-floor, in consequence of the action of marine worms, to those which Darwin has so carefully studied upon the terrestrial surface as resulting from the action of earthworms. In both cases we recognize an impressive illustration of the action of seemingly insignificant agents in producing results of the greatest magnitude.

While the clays in the less profound portions of the ocean-floor are, as a rule, characterized by a dark-blue color, there

are certain areas, like that off the East coast of South America, where red and variegated tints, like those of our Trias, Permian, and Plastic-Clay formations, are found to prevail. In these cases the iron is evidently in a different state of oxidation and combination to that of the blue clays. the blue clays. In all the deepest portions of the ocean, similar tints of red and chocolate-brown characterize the argillaceous deposits, that seem to be very slowly accumulating there. There in evidence that even at these extreme depths (3,000 to 4,000 fathoms and upward) living beings exist in considerable abundance, in spite of the extreme cold, the great pressure, and total absence of light. So that the separation of the iron from its state of solution may even here be due to the action of living organisms, though the slowness with which accumulation takes place leads to the oxidation of the iron.

On these deepest parts of the oceanfloor, however, we find very remarkable chemical deposits, which may well engage the attention of chemists and geologists, as throwing light upon the curious actions taking place in the profoundest recesses of the sea-bed. First among these we may mention the curious crystalline masses of zeolites, that are sometimes found scattered throughout the red mud, and occasionally forming no inconsiderable proportion of its mass.

These zeolitic minerals are known to geologists as the constant result of the action of water upon the silicates that compose volcanic rocks, and are usually found in the steam holes and other cavities of lavas, which through long periods of time have been subjected to the action of permeating waters. Daubrée has shown that the same minerals have been formed at Plombières and other localities during historical times, by the action of more or less heated spring waters upon the brick- and concrete-structures erected by the Romans to serve as conduits for them. The chemical action which produces these zeolites on the ocean-floor must take place at temperatures but little above that of the freezing point of fresh water; but it is not improbable that the great pressure, amounting to between three and four tons to the square inch, may be a substitute for the want of an elevated tem

perature in promoting chemical change. Even under much more moderate pressures, however, we find in the " glauconite" casts of the shells of the foraminifera, clear evidence that chemical action is going on upon the sea-bed, by which the brown amorphous mud is converted into a crystalline a crystalline green silicate.

Perhaps the most interesting of all the chemical deposits on the deeper parts of the ocean-floor are those curious and irregular nodules, varying in size from a pea to an orange, which are composed of the hydrated oxides of manganese and iron. Although very variable in composition, we may state the average proportions of their ingredients as follows: -manganese dioxide 25 per cent., iron peroxide 15 per cent., water 30 per cent., and various silicates and foreign substances entangled in their mass 30 Careful analyses have shown that no less than twenty-six of the chemical elements can be detected in these remarkable concretions, and among them such rare ones as thallium, molyb. denum, tellurium, tellurium, and vanadium. Nickel, cobalt, tin, copper, and lead are among the more common metals found in these concretionary masses, and lithium, barium, and strontium among the metals of the alkalies and the alkaline earths. Not only do we find nodules, the internal structure of which indicates slow and gradual deposition, but teeth, bones, and other objects occur, either surrounded by a coating or completely impregnated, with the same mixed oxides.

The origin of these accumulations of manganese oxide, combined with so many other rare substances, constitutes a problem as difficult as it is fascinating. It is true that manganese is a metal far more widely distributed than is often supposed; indeed, careful analysis almost always shows that where iron is present manganese can be detected also; but in the great majority of cases the proportion of manganese in rocks and other natural products does not exceed one-tenth, or even one-twentieth, of that of the iron. All analyses of sea-water show the proportion of iron in it to be extremely small, while manganese is seldom, if ever, traceable by direct analysis, either in sea-water itself, in the salts left

by evaporation of sea-water, or in the ashes of plants and animals that have lived in that water. It is very doubtful if the proportion of manganese in sea-water ever reaches one part in a million, and it is far more probable that the proportion would be represented by one part in many millions of the solvent.

How, then, are we to account for the separation of this minute proportion of manganese to form the concretions in which it is the most abundant constituent? Mr. Murray has suggested that the manganese of the nodules has never been distributed in solution through the oceanic waters, but has been derived directly from the decomposition of volcanic rocks on the sea-bed. This view, however, has been rejected as inadmissible by Mr. Murray's colleague, Professor Renard, and by most authors who have devoted their attention to the problem. Almost all of these have agreed that the manganese must have existed in the first instance dissolved in sea-water, probably in the form of carbonate, and have been separated by some chemical process going on upon the ocean-floor.

The soundings made by Murray and Buchanan upon the west coast of Scotland have shown the manganese oxide, mingled in various proportions with iron oxide, is very constantly present in marine muds, even at moderate depths; and if we admit an organic origin for the iron, is it possible to avoid the conclusion that the manganese and other rarer metals must have been separated from their state of diffusion in seawater by the same agency?

All the facts collected by the deep-sea exploring expeditions point to the conclusion that accumulation of material is going on with the most extreme slowness at these abysmal depths where the manganese nodules are found in greatest abundance, and it may well be that these slowly accumulating muds have been passed through the bodies of marine worms or other organisms an almost infinite number of times. At each passage of the clay through the organism a small addition of manganese and iron oxides would be made to the mass by the action of the living structure on the sea-water, and thus in the course of time these oxides might be sufficiently concentrated

to build up, by concretionary action, the remarkable nodules on the ocean-bed.

Such action would be in complete analogy with processes going on both in fresh and salt water, by which calcareous, silicious, phosphatic, and ferruginous deposits are being every where formed in the waters of the ocean, while all theories of the direct separation of the manganese and rarer metals from their state of excessively dilute solution

in sea-water by chemical reactions appear to me to be beset with the greatest difficulty. All the observations that have been made in recent years upon the deposits of the ocean-floor point to one conclusion, namely, that where materials have once passed into a state of solution in the waters of the sea they can only be separated from it in the open ocean by the wonderful action of living organisms.-Fortnightly Review.

PEOPLE'S BANKS.

BY T. MACKAY.

MR. H. W. WOLFF has recently put within the reach of English readers a most interesting account of the history and constitution of Co-operative Banks in German and Italy.* For fuller in formation on this subject the reader is referred to this excellent work. The object of the following pages is merely to discuss how far these institutions of popular credit are fitted to take a place among the provident associations of the poorer classes of this country.

Before considering any proposal for the establishment of popular credit, there is a preliminary question to be asked. What is the function of Credit in the wealth-producing mechanism of industrial society? No English writer seems to me to have apprehended this matter so profoundly, and at the same time explained it so lucidly, as Mr. H. D. Macleod, in his various works on the theory of banking and credit. Briefly, Credit is Capital. By means of credit a man is enabled to pass into currency as capital his mere promise to pay. The value of such a promise to pay rests on the trustworthiness and industry of the promiser and on the general proposition that human effort properly applied is productive of harvest sufficient to reward all who contribute to the result. A man, therefore, who possesses credit capitalizes his reputation, and acquires thereby a better equipment for the enterprise in which he is engaged. If the operation is successful a solid addition

*People's Banks. By H. W. Wolff. Longmans, 1893.

to the wealth of the community is made, if it is unsuccessful a certain amount of loss is sustained; but, as far as the country at large is concerned, it is immaterial whether the capital consisted in hard cash or material actually hoarded by the operator, or in credit advanced to him by other tradesmen, or by credit associations. Credit, and the vast addition to the national wealth thereby created, can only arise in a settled state of society. It is based on the general trustworthiness and the mutual confidence of the persons who avail themselves of its assistance. It depends on the general law that the punctual performance of contract is the rule and not the exception. A farmer trusts his seed to the ground in the assurance that the natural sequence of seed-time and harvest will be maintained. So the granting of credit in the ordinary business of the world is based on the assumption that if the industry of men of character and intelligence can be set in motion a harvest of profit will be reaped for all concerned-for consumer, for laborer, and for capitalist. Human energy, which in a highly developed state of industry can only be set in motion with the assistance of capital (and in many cases the capital will take the form of credit), is just as prolific a source of profit or harvest as the action of the seasons in agriculture.

The illustration most frequently given of the beneficial results of a wellorganized system of credit is the banking system of Scotland. Mr. Macleod has pointed out that 150 years ago Scot

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