DEEP-SEA DREDG1NGS.*
FEW, probably, are altogether devoid of a natural and instinctive desire to obtain some acquaintance with the world in which we live, though it is not given to many to gratify the desire to any extent. From the earliest dawn of knowledge men have occupied themselves in the task of successfully combating the mechanical difficulties which nature has thrown in the way of those who seek to penetrate her secrets, and much has been effected in this direction. For centuries there existed no greater obstacle to the .acquisition of physical knowledge than the exceedingly imperfect and tedious means of locomotion which were alone at the disposal of the philosopher. This has been overcome ; and it would not be easy to over-estimate the share which our railways have had in the rapid development which we have seen of late years in such sciences as geology and zoology.
ith all the mechanical appliances, however, of modern science there still remain vast portions of the terraqueous globe =of which the investigation, except in the most fragmentary manner, appears to be almost impossible. Whole countries are buried beneath an ever-shifting yet permanent sheet of ice ; large portions of others are rendered almost impassable by arid sands and want of rain ; others are clothed for hundreds of miles together with dense and trackless forests ; and above some 15,000 feet our loftiest mountain-chains are practically inaccessible to the observer. A priori, one would be inclined to believe that the difficulties in the way of scrutinizing the bed of the deep sea would be greater and more insurmountable than any of the, above, and until .very
lately this has been found to be the case. Recently, however, attempts have been made, in different parts of the world, and by :
different observers, to solve this problem ; and enough has been done to show that a new and almost inexhaustible vein of inquiry has been opened, the results of which it would be hazardous to predict. Before examining the latest and most successful of these attempts, let us see what had been already accomplished in this direction.
Our knowledge of the inhabitants of the ocean has been almost entirely derived from such observations as can be made between tide-marks, from the use of the sounding apparatus, or from the operations of the dredge. The first of these obviously offers an extremely limited field for investigation, and the second, though applicable to great depths, can do no more than bring to the surface the small portion of the sea-bottom upon which it drops, together with such animals as may chance to be upon it ; and even this is a very recent improvement. From its great collecting power, and from the amount of surface which it is capable of covering, the dredge has naturally been the favourite instrument of the marine zoologist, and to it he owes almost as much as the physiologist to the microscope. Much, however, remained to be done even in this direction, Until last year dredging had never been carried on at depths exceeding some 300 fathoms, and was confined as a rule to much shallower tracts. This was partially due to the great difficulty of manipulating the dredge at great depths, and partially, no doubt, to the very prevalent opinion that the bottom of the deep sea would be found to be a lifeless solitude, barren of spoils to the naturalist. The late Professor Edward Forbes, oire of the most accomplished zoologists of modern times, concluded from his researches that a zero of animal life in the sea would be found at 300 fathoms, referring elsewhere to all beyond this depth as " an abyss where life is either extinguished, or exhibits but a few sparks to mark its lingering presence." The first blow to this widely accepted doctrine was given by Captain Ross, in his Arctic Expedition (1818), who brought up a living starfish from a depth of one thousand fathoms by means of the sounding-line. Similar results were afterwards obtained, but at smaller depths, by Sir James Ross and Mr. Harry Goodsir ; but they attracted little attention at the time, and were soon forgotten. The first real steps towards the solution of this question were made by Professor Bailey of the United States, and by Professor Huxley and Dr. Wallich at home. These observers proved, by means of soundings, that the bed of the Atlantic at depths of from 1,000 to 2,000 fathoms was composed almost entirely of the calcareous cases of certain minute Protozoa, and of the flinty envelopes of one of the lowest orders of plants ; the former of these, at any rate, being beyond a reasonable doubt truly resident at this enormous depth. Quite recently the existence of animals of a higher grade of organization at great depths in the ocean has been established by the researches of Professor Sara, and Count Pourtales of the United States Coast Survey. In neither of these cases, however, though some very striking facts were brought to light, were the dredgings carried on at depths of more than 500 fathoms.
The pamphlet at present before us is the record of the results of a systematic attempt to dredge the deep sea, carried on by Dr. Carpenter and Professor Wyville Thomson, a surveying ship with all the necessary appliances having been placed at their disposal by the Lords Commissioners of the Admiralty. The ground chosen for the cruise was the deep channel between the North of Scotland and the Faroe: Islands, and though the weather was very unfavourable and the time limited, nevertheless some highly curious and valuable discoveries have been made. The special object of the expedition was to determine what living beings—If any—inhabited the deeper portions of this area; and it is sufficient to state that this object was fully attained by the discovery of many curious forms of animal life at depths of from 500 to 60 fathoms. Amongst these, besides an abundance of lower forms, there were many examples of zoophytes, starfishes, shell-fish, and crustaceans.
So much for the facts, as far as this portion of the inquiry i3 concerned; and now for the deductions which may be drawn from the facts. In the fi rat place, we may now regard it as fullyestablished that there exists " a varied and abundant submarine fauna at depths which have been generally supposed to be altogether asoic, or occupied only by animals of a very low type." As a necessary consequence of this, we must give up the long accepted belief that great baihymetrical pressure, that is to say, the pressure caused by a great mass of superincumbent water, is necessarily destructive or prejudicial to the higher forms of animal life. It appear, on the contrary, from what we now learn, that " the distribution c the animal life of the seas beyond the littoral zone is more closely related to the temperature of the water than to its depth," just as the distribution of plants upon mountain chains is regulated, not by the elevation, but by the temperature, which is merely a secondary result of the elevation. More extraordinary, however, than the abundance of animal life at these great depths is its character ; and here we arrive at one of the most striking discoveries of modern science, though it is one which will have to be worked out in greater detail before we can reason confidently upon it. It appears, namely, that these hitherto unexplored abysses of the ocean have constituted asylums, so to speak, for forms of life which are elsewhere extinct, and are only known to us as characterizing some long-past geological epoch ; not to speak of others up to this time believed to be limited to particular localities or altogether new to science. To state this result more specifically without entering into technical details is difficult, but it appears certain that not only is the bottom of the North Atlantic at great depths covered with a deposit in all its essential characters closely resembling chalk, but that the higher animals now known to inhabit this area are also closely allied to, and in some cases even inseparable from, species which lived during the Cretaceous epoch. Enough, at any rate, has been discovered to render it certain that more extensive researches are only likely to confirm and amplify this important generalization. We may just allude here toanother curious question, which has been opened up by these discoveries. From what quarter do the denizens of the deep sea derive their food ? All, clearly, cannot be carnivorous, and we have as yet obtained no indication that vegetable life is possible at these great depths. In fact, the apparent impossibility of the luminous rays of the sun penetrating far beneath the surface of the sea, to say nothing of the actinic or chemical rays, would seem to preclude the existence of any but the very lowest forms of plants ; and these are not only very minute, to begin with, but have been obtained in very small numbers. To meet this difficulty, Dr. Carpenter suggests, with a great show of probability, that one of the most lowly organized and at the same time most abundant of the inhabitants of the deep sea may have " so far the attributes of a vegetable, that it is able to elaborate organic compounds out of the materials supplied by the medium in which it lives, and thus to provide sustenance for the animals imbedded in its midst."
Besides the above-mentioned additions to zoology, Drs. Carpenter and Wyville 'Thomson have succeeded in establishing a remarkable physical law regarding the temperature of the sea. To the almost universal law that heat causes expansion, and cold contraction, of the particles of a body, water has long been known to constitute a striking exception. When any body of fresh water is exposed to a reduction of temperature, as the surfacelayer becomes colder than the remainder of the fluid, it becomes likewise heavier, and sinks, therefore, to the bottom, its place being supplied by a warmer and consequently lighter stratum. This process is repeated until the temperature has sunk to .39° Fahr., when the law ceases to act. Below this point—termed the maximum density of water—any additional reduction of temperature causes expansion, instead of contraction, and consequently the surface-layer becomes and remains the lightest, and does not sink as before to the bottom. It is obvious that, if this deviation from the regular law were not provided for iu the case of water, all our lakes and rivers would begin to freeze from the bottom upwards, and would, in our climate, become ultimately entirely converted into ice. It has always been believed that what we have just stated held good for all water, whether fresh or salt ; hence the statement of Sir J. Herschel! that, " in very deep water all over the globe a uniform temperature of 39° Fehr. is found to prevail ;" as would almost necessarily be the case if the maximum density of salt water, like that of fresh, were reached at this temperature. We now know, however, that the law must be differently stated for sea-water. By sending down thermometers attached to the sounding-line, Drs. Carpenter and Thomson have proved that in certain areas—supposed to be those traversed by cold currents from the Polar regions—the tempera. ture at the bottom was as low as 32° Fehr., whilst that of the surface might be as high as 53° Fahr., a difference of more than 20°. This great difference is easily accounted for by the existence of cold Polar and warm Equatorial currents; whilst the very low temperature of the bottom is explained by certain experiInenta of Despretz, establishing beyond a doubt the fact that "sea water, in' virtue of its saline impregnation, contracts continuously down to its ordinary freezing-point, which is below 28° Fahrenheit."
in We have been compelled to touch lightly on the many interest
omit others altogether ; but we have said sufficient to warrant the opinion that his report to the Royal Society embodies some most remarkable discoveries, which are not only valuable per se, but lead to some very important and striking generalizations. We trust that the inquiry thus happily begun will be followed out, and we can hardly err in our expectation that we shall find ourselves to be merely on the threshold of an investigation, long, perhaps, and difficult, but promising to repay us ultimately with the most brilliant results.
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