452 



NATURE 



\^AugUSt 22, 1878 



drifted to latitudes of 65° or 64° south, the bottom of the berg, 

 the surface which forced itself glacier-like over the land, just 

 reaches the layer at which the temperature of the water dis- 

 tinctly rises ; and is rapidly melted, and the pebbles and land 

 debris with which it is more or less charged are precipitated. 

 That this precipitation takes place all over the area where the 

 icebergs are breaking up, constantly and to a considerable extent, 

 is evident from the fact that the matter brought up by the sound- 

 ing instrument and the dredge is almost entirely composed of 

 such deposits from ice ; for diatoms, foraminifera, and radio- 

 larians are present on the surface in large numbers, and unless 

 the deposit firom the ice were abundant it would soon be covered 

 and masked by the skeletons of surface organisms. 



The curious question now arises, what is the cause of the 

 uniform height of the southern icebergs — that is to say, what is 

 the cause of the restriction of the thickness of the free edge of 

 the ice-cap to 1,400 fathoms ? I have mentioned the gradual 

 diminution in thickness of the strata of ice in a berg from above 

 downwards. The regularity of this diminution leaves it almost 

 without a doubt that the layers observed are in the same category, 

 and that therefore the diminution is due to subsequent pressure 

 or other action upon a series of beds, which were at the time of 

 their deposition nearly equally thick. About 60 or 80 feet from 

 the top of an iceberg, the strata of ice a foot or so in thickness, 

 although of a white colour and thus indicating that they contain 

 a considerable quantity of air, are very hard, and the specific 

 weight of the ice is not much lower than that of layers three 

 inches thick nearer the water-line of the berg. The upper 

 layers have been manifestly produced by falls of snow after the 

 berg has been detached. 



Now it seems to me that the reduction in thickness cannot be 

 due to compression alone, but that a portion of the substr.nce of 

 the lower layers must have been removed. It is not easy to see 

 why the temperature of the earth's crust, under a widely extended 

 and practically permanent ice-sheet of great thickness, should 

 ever fall below the freezing-point ; and it is a matter of observa- 

 tion that at all seasons of the year vast rivers of muddy water 

 flow into the frozen sea from beneath the great glaciers which 

 are the issues of the ice-sheet of Greenland. Ice is a very bad 

 conductor, so that the cold of winter cannot penetrate to any 

 great depth into the mass. The normal temperatiu-e of the sur- 

 face of the earth's crust, at any point where it is uninfluenced 

 by cyclical changes, is at all events above the freezing-point, so 

 that the temperature of the floor of the ice-sheet would certainly 

 have no tendency and fall below that of the stream passing over 

 it. The pressure upon the deeper beds of the ice must be 

 enormous at the bottom of an ice-sheet 1,400 feet in thickness — 

 not much less than a quarter of a ton on the square inch. It 

 seems, therefore, probable that under the pressure to which the 

 body of ice is subjected a constant system of melting and regela- 

 tion is taking place, the water passing down by gravitation from 

 layer to layei- until it reaches the floor of the ice-sheet, and 

 finally working out channels for itself between the ice and the 

 land, whether the latter be subserial or submerged. 

 r I should think it probable that this process, or some modifica- 

 tion of it may be the provision by which the indefinite accumu- 

 lation of ice over the antarctic continent is prevented and a cer- 

 tain uniformity in the thickness of the ice-sheet maintained — 

 that in fact ice at the temperature at which it is in contact with 

 the surface of the earth's crust within the antarctic regions can- 

 not support a column of itself more than 1,400 feet high without 

 melting. It is suggested to me by Prof. Tait that the thickness 

 of the ice-sheet very probably depends upon its area, as the 

 amount of melting through squeezing and the earth's internal 

 heat, will depend upon the facility of the escape of the water. 

 The problem is, however, an exceedingly complex one, and we 

 have perhaps scarcely sufficient data for working it out. 



Tlie Fauna of the Deep Sea.— I can scarcely regret that it is 

 utterly impossible for me on this occasion to enter into any 

 details with regard to the relations of the abyssal fauna, the 

 department of the subject which has naturally had for me the 

 greatest interest. Recent investigations have shown that there 

 is no depth limit to the distribution of any group of gill-bearing 

 marine animals. Fishes, which, from their structure and from 

 what we know of the habits of their congeners, must certainly 

 live on the bottom, have come up from all depths, and at all 

 depths the whole of the marine invertebrate classes are more or 

 less fully represented. The abyssal fauna is of a somewhat 

 special character, differing from the fauna of shallower water in 

 the relative proportions in which the different invertebrate types 



are represented. It is very uniform over an enormously extended 

 area, and in this respect it fully confirms the anticipations of 

 the great Scandinavian naturalist Loven, communicated to this 

 Association in the year 1844. It is a rich fauna, including 

 many special genera and an enormous number of special species, 

 of which we, of course, know as yet only a fraction ; but I do 

 not think I am going too far in saying that from the results of 

 the Challenger expedition alone the number of known species in 

 certain classes will be doubled. The relations of the ab3rssal 

 fauna to the faunae of the older tertiary and the newer mesozoic 

 periods are much closer than are those of the faunce of shallow 

 water ; I must admit, however, that these relations are not so 

 close as I expected them to be — that hitherto we have found 

 living only a very few representatives of groups which had been 

 supposed to be extinct. I feel, however, that until the zoolo- 

 gical results of several of these later voyages, and especially 

 those of the Challenger, shall have been fully worked out, it 

 would be premature to commit myself to any generalisations. 



I have thus attempted to give a brief outline of certain defen- 

 sible general conclusions, based upon the results of recent re- 

 search. Some years ago, certain commercial enterprises, involv- 

 ing the laying of telegraph cables over the bed of the sea, 

 proved that the extreme depths of the ocean were not inacces- 

 sible. This somewhat unexpected experience soon resulted in 

 many attempts, on the part of those interested in the extension 

 of the boundaries of knowledge, to use what machinery they 

 then possessed to determine the condition of the hitherto un- 

 known region. This first step was naturally followed by a deve- 

 lopment of all appliances and methods bearing upon the special 

 line of research; and within the last decade the advance of 

 knowledge of all matters bearing upon the physical geography 

 of the sea has been confusingly rapid — so much so, that at this 

 moment the accumulation of new material has far outstripped 

 the power of combining and digesting and methodising it. This 

 difficulty is greatly increased by the extreme complexity of the 

 questions, both physical and geological, which have arisen. 

 Steady progress is, however, being made in both directions, and 

 I trust that in a few years our ideas as to the condition of the 

 depth of the sea may be as definite as they are with regard to 

 regions to which we have long had ready access. 



Section G. 

 mechanical science. 



Opening Address by the President, Edward Easton, 

 C.E. 



On the Conservancy of Rivers and Streams. 



By the conservancy of rivers and streams I mean the treat- 

 ment and regulation of all the water that falls on these islands 

 from its first arrival in the shape of rain and dew to its final 

 disappearance in the ocean. 



I had at first, in my ignorance, contemplated treating the 

 subject in a still wider manner by referring to the rivers and 

 streams of other countries; but I soon found that the vast 

 extent of the field to be traversed would make it extremely un- 

 likely that I could, with any satisfactory result, attempt the 

 more restricted task which I have now before me. 



The question of the conservancy of rivers and streams involves 

 the consideration of their regulation for the following principal 

 purposes : — 



1st. For the supply of pure and wholesome water for the 

 domestic and sanitary wants of the population. 



2nd. For the supply of water of proper quality and sufficient 

 quantity for industrial purposes. 



3rd. For the proper development of water power. 



4th. For the drainage and irrigation of land. 



5th. For navigation and commerce. 



6th. For the preservation of fish. 



Until the appointment last year of the Select Committee 

 presided over by the Duke of Richmond, no attempt, as far as 

 I am aware, has been made to grapple with the question as a 

 whole, and the Report made by them omitted to deal with, at 

 least, two of the objects I have indicated as being necessary to 

 the proper dealing with the subject. 



The recommendations made in the Report of that Committee 

 were most important, and will, if carried out, remove many of 

 the difficulties which stand in the way of a complete system of 

 conservancy of our rivers. 



