BOOKS.

AGASSIZ'S " THREE CRUISES OF THE BLAKE."* IMPORTANT as are the subjects treated in this profusely illustrated work, the abstruse nature of most of the problems with which he has to contend will, we fear•, for the present debar the general reader from embarking with the accom- plished author• to investigate the countless questions of interest presented by the waters over which he cruised. It is nearly forty years since Mr. Alexander Agassiz—Dr. Agassiz we might in this country call him, as one of our ancient Univer- sities has honoured itself by so dubbing him—was introduced by his celebrated father•, the late Professor Louis Agassiz, to the then very little understood principles of what in this work for the first time receives the definite name of " Thalasso- graphy;" but, after abandoning its active pursuit for a while, in 1877 he accepted an invitation from the Superintendent of the United States Coast Survey to contimse, under its auspices, the work in which he had begun his biological studies. A steamer•, the Blake,' of 350 tons burden, was placed at his disposal, and the winters of 1877-78 and 1878-79, together• with part of the summer• of 1880, were devoted by him to the " Three Cruises" with the principal results of which these hand- some volumes make us acquainted. The first two of these cruises were mainly in West Indian waters, and the last along the East Coast of North America, from Maine to South Carolina, extending seaward to the course of the Gulf Stream.

Of narrative there is in this work little, and those who look only for• glowing descriptions of tropical scenery, or• of the verdant shores of the always beautiful Antilles, will be dis- appointed. In the most matter-of-fact way, the introduction tells us the points of departure and arrival of the different cruises, and even these matters sparingly; but those who will look through the waters and see what is revealed of them by the tow-net, the trawl with its "tangles," and the deep-sea lead, will find on almost every page wherewith to reward their trouble, and set their thoughts on the hidden wonders of the abyss,—not only on the strange forms of life which exist between the floor of the ocean and its surface, but on its structure, irregularities of level and configuration, the changes which it has undergone in times long past, as well as those now in progress and yet to come. Themes like these, it is needless to observe, are at present, and long will be, inexhaustible. To compare small things with great, the vicis- situdes of parts of our own English coast, often observable in a single generation, we have here repeated on a vastly extended

• A Contribution to American Thatassography Three Cruises of the United States Coast and Geodetic Surrey Steamer ' Blake,' in the Gulf of Mexico, in the Caribbean &a, and along the Atlantic Coast of the United States, from 1877 to 1889. By Alexander Agassiz. 2 vols. London: Sampson Low. 1::3.

scale, and with effects that in the course of ages are almost incalculable. The term Thalassography " has been happily coined by our author to express in a single word all that is comprised by such a limitless study as this.

The first chapter is devoted to an account of the equipment of the Blake,' and deserves the greatest attention from all those who in future may go down to the sea in dredging-ships and occupy their business in the abyssal waters ; but it is too technical for particular notice here, and we need only remark that each successive expedition for• thalassographical ends gives rise to some improvement of the complicated machinery and appliances required. Even some of the instruments used so lately as in the voyage of the' Challenger' have been found to be in several respects defective, and have been superseded by others which the ever•-fertile ingenuity of the engineer• has supplied in their place. The mere substitution of steel wire for hemp in the dredging-lines has so much facilitated opera- tions that, since its introduction, they may be almost said to have been revolutionised. The next chapter gives a succinct and, so far as we can judge, an impartial " Historical Sketch of Deep-Sea Work," in which there is now hardly a civilised Government that has not taken some share ; but to our readers, at this juncture, the chapter on the Florida reefs will perhaps afford more interest. According to our author (Vol. I., pp. 55-56),-

" All naturalists who have visited the Florida reefs have felt the difficulty of applying Darwin's theory of reef formation to the peculiar conditions existing along the Straits of Florida. Agassiz [the father], Le Conte, and E. B. Hunt have each in succession attempted to explain, from a different standpoint, the mode of formation of the Florida reefs. Agassiz stated, and his statement was afterwards confirmed by Le Conte, that the Florida reefs had a distinctive character•, and could not be explained by subsidence, to which cause Darwin had ascribed the formation of barrier reefs in general."

And again (Vol. I., p. 61) :- " There is practically no evidence that the Florida Reef, or any part of the southern peninsula of Florida which has been formed by corals, owes its existence to the effect of elevation ; or that the atolls of this district, such as those of the Marquesas or of the great Alacran Reef, owe their peculiar structure to subsidence."

Now, we cannot help remarking, with all deference to our author and to some others who have written on this very interesting subject, that it may, after all, be Mr. Darwin's definitions of a " barrier•-reef " and of an atoll " that need amending. There is, to say the least, an appearance of begging the question in applying these terms—which he was the first to bring into use—to structures which his definitions (given, be it remembered, more than half-a-century since), if read in the light of later discoveries, would exclude. But we have no intention of taking part in the controversy which has been raging, and we confine ourselves to quoting our author's summing-up of the case as regards this particular instance,— a summing-up which displays, in marked contrast to the in- temperate zeal of some of the disputants, the best qualities of the scientific man (I., pp. 77-78) :-

" Undoubtedly, Darwin's theory of reef formation presents a sound and admirable exposition of the grander causes which have brought about the elevation or subsidence of large tracts to a level favorable for coral growth ; but at the time he wrote upon this subject, the formation of extensive limestone banks, built up by the animals living on the bottom, and constantly strengthened and increased by the attendant phenomena of winds and currents, was little understood. These facts have been brought into notice and emphasized by recent deep-sea explorations. Darwin, how- ever, when examining maps of the West Indies, had been struck by the probable connection between the areas of deposition of the great banks marked upon the charts and the course of the sea- cur•rents. He naturally explained the steep slopes, abruptly dropping from comparatively shallow plateaux to great depths, by what is known to occur wherever great masses of sediment are found, and he therefore considered these plateaux to be submerged mountains. Such they are, in a certain sense ; not wholly built, however, as Darwin supposes, of sediment, but in great part also of the remains of the innumerable animals living and dying upon them. The nucleus of these banks has probably been formed around the shores of promontories subjected to the most active play of the great oceanic currents. At the time when Darwin wrote, and when we knew little of the limestone deposits formed by the accumulation of the debris of mollusks, echinoderms, polyps, and the like, upon folds of the earth's crust, the formation of the basal parts of barrier reefs was difficult of explanation. The evidence gathered by Murray, Semper, and myself, partly in districts which Darwin had already examined, and partly in regions where his theory of reef formation never seemed to Snd its proper application, has in a measure removed this difficulty. It all tends to prove that we must look to many other causes than those of elevation and subsidence for a satisfactory explanation of coral-reef formation. All-important among these causes are the prevailing

winds and currents, the latter charged with sediment which helps to build extensive plateaux from lower depths to levels at which corals can prosper. This explanation, tested as it has been by penetrating the thickness of the beds underlying the coral reefs, seems a more natural one, for many of the phenomena at least, than that of the subsidence of the foundation to which the great vertical thickness of barrier reefs has been hitherto referred. Still, it is difficult to account for the great depth of some of the lagoons—forty fathoms—on any other theory than that of subsidence."

Leaving this undecided question, we pass to a topic that may strike our readers with that very rare thing in these days—a novel sensation. In our second paragraph we spoke of "the floor of the ocean "—a harmless phrase in reality, but one capable of conveying a false impression, for by it most people might be led to suppose that we meant them to infer that this floor, like most floors with which they were acquainted, was flat. We wonder how many persons have ever formed a con- ception of what it is like, or of the hidden inequalities of the mighty deep. All have heard of the " roof of the world"— how many have dreamed of what we may call its " cellars ? Those who can visualise the teachings of the sounding-line may form a notion of it. Hear again our author (Vol. I., p. 104) :— " What can be more impressive than the stupendous slope of over twelve thousand feet that forms the eastern edge of the

Bahama Bank, stretching from the Great Abaco nearly unbroken as far as the Virgin Islands, with high passes between Porto Rico and San Domingo, and a deep cation between San Domingo and the southern end of the Bahama Bank ? The northern ex- tremity of this cliff, over seven hundred miles long, forms the edge of a huge triangular plateau, five hundred miles by two hundred and fifty, scarcely rising above the level of the sea, and flanked on its western side by the high chains of Cuba. Its eastern extremity falls into the edge of a sink, of a depth of over four thousand fathoms, and culminates at a horizontal distance of less than eighty miles in a summit on the island of Porto Rico, no less than thirty thousand feet above the lowest point of that depression.

We may imagine for a moment that we are taking a bird's-eye view of this whole district, and look down upon the comparatively level plains of the Atlantic to the eastward of Barbados The southern slope of this part of the West India Islands chain is fully as steep as the northern. At the western extremity of San Domingo, the southern line of mountains extends toward Jamaica, and that part of the chain is deflected to the southward, having also a much gentler slope, and forming the edge of the Pedro Rosalind Bank, the extension of the Honduras Mosquito coast, which divides the Caribbean into an eastern and western basin. After passing the Pedro Rosalind Bank,—the divide between the Western and Eastern Caribbean,—one comes into the valley of the Grand Cayman, the eastern extremity of which is flanked on the one side by the Blue Mountains of Jamaica, on the other by the coast range of Southern Cuba, the highest summits of which rise fully twenty-seven thousand feet above the deepest point of ' Bartlett Deep,'—the extension of the Cuban side of the valley being formed by peaks, often rising to over twenty thousand feet from the bottom of the valley. Compared to such panoramas, the finest views of the Alps sink into insignificance ; it is only when we can get a view of portions of the Andes from the sea-coast, or such a panorama as one has from Darjiling, facing the Kinchinjinga range, which towers fully twenty-six thousand feet above the level valley at its base, that we get anything approximating to it in grandeur."

Glorious as is this vision to the eye of science, it has its set-off :— " The monotony, dreariness, and desolation of the deeper parts of this submarine scenery can scarcely be realised. The most barren terrestrial districts must seem diversified when compared with the vast expanse of ooze which covers the deeper parts of the ocean,—a monotony only relieved by the fall of the dead car- casses of pelagic animals and plants, which slowly find their way from the surface to the bottom, and supply the principal food for the scanty fauna found living there. Nearer to the continental masses we find the slopes inhabited by a more abundant and more varied fauna, increasing in variety and numbers according to the amount of food available. But no matter how varied or how abundant life may be, the general aspect of the slopes must be dreary in the extreme, and can only be compared in character to those higher mountain regions where we find occasional fields of wild-flowers and low shrubs, or to those zones lying beyond the limits of forests, whose vegetation is scanty and poor, and forms

but a slight covering to the earth's surface It requires but little imagination to notice the contrasts, as we pass from the shallow littoral regions of the sea,—full of sunlight and move- ment, and teeming with animal and vegetable life,—into the dimly lighted, but richly populated continental zone; and further to imagine the gradual decrease of the continental fauna as it fades into the calm, cold, dark, and nearly deserted abyssalregions of the oceanic floors at a distance from the continents. It is like going from the luxuriant vegetation of the tropical shore line— the region of palms, bananas, and mango—into the cooler zone of oaks and pines, until we pass out into the higher levels, with their stunted vegetation and scanty fauna, and finally into the colder climate of the bleak regions of perpetual snow." (Vol. I., pp. 106-7.)

It has been the fashion with many latter-day writers to• decry the theory of the late Edward Forbes, formulated, be it

remembered, on researches prosecuted more than forty years ago, and only in British and Mediterranean waters. It seems to us, as shown by the preceding extract and several other passages we could cite, had we space, from this work, that he

was justified in believing that there was a zone in which animal life was almost non-existent ; but that his mistake-

was in not sinking that zone deep enough. The rudeness of the only tackle at his command was in great measure the cause of his underrating the depth at which the ocean becomes

nearly azoic. It is true that we now know of far deeper- soundings and searchings which had been already made during the celebrated Antarctic voyage of the Erebus' and Terror,' though we believe that no particular account of the results ob- tained has ever been, or is ever likely to be, published.* What- ever they were, there is no evidence that Forbes had any acquaintance with them. Against him our author makes no- charge: indeed, he justly calls him "the most brilliant naturalist perhaps of his time ;" but there can be no doubt that towards him a very ungenerous feeling has been exhibited. It is a mere truism to say that it is easy for a zoologist to be wiser than his predecessors ; but then, every zoologist ought to remember that his successors will be wiser still. The case is similar with respect to the ancient belief in the Gulf Stream and its potent effects. Only a few years ago, a great authority busied himself not merely in speaking disrespectfully of it—as Sydney Smith's acquaintance did of the Equator—but even in striving to show that, if it existed at all, it was of no account whatever, and that all we had to be thankful for in this country was the absence of an Arctic current such as prevails along the opposite shores of the Atlantic, the icy breath of which keeps Newfoundland frost-bound for eight months in the year, and assimilates the winter-temperature of Philadelphia to that of Copenhagen. Yet such is the curious crowding of the cold isotherms on the Eastern Coast of the United States, that, thanks to the Gulf Stream, a few hours' steaming in a south- easterly direction will convey the shivering and sneezing Bostonian from a temperature below the freezing-point, and the New Yorker or Philadelphian from a temperature not much higher, to one of between 60 and 70 degrees of Fahrenheit's scale, wherein (sea-sickness apart) mere existence is a pleasure. This fact is set forth, we do not pretend to say for the first time, in the present work (Vol. I., fig. 168) ; but hereby we have to make a grave complaint, though the only one, against our author. His maps and charts are simply abominable Accurate they doubtless are if we could see them ; but they are nearly all reductions from larger drafts, on which the writing and other graphic marks may have been plain enough. He has, however, forgotten that in lessening their proportions, the lettering has become illegible to the naked eye, and the annoyance of having to use a magnifying glass whenever a map or chart is to be consulted, is as worrying to any one but a German as it is unnecessary. This grievous blemish is rendered all the more conspicuous by comparison with the woodcuts (as we suppose they must be called, though probably wood was never used in their execution) of the different animals figured. These illustrations are of exquisite beauty, and of absolute fidelity, since most of them are obviously reproduced from photographs, while (as we said at the beginning) they are profuse in number. The second volume of the work is in itself a submarine museum, and we are not at all sure that in many cases more knowledge may not be gained from the well-chosen figures than from the very specimens which are portrayed.