June 1, 1892.] 



KNOWLEDGE 



117 



the Adriatic with the main waters of the Mediterranean 

 Sea. 1 



It has been found that the temperature of the Medi- 

 terranean Sea bed is by no means constant, and, according 

 to some authorities, varies slightly in accordance with the | 

 mean temperature of the winter preceding the season in 

 which the temperatures of the sea bottom are taken. ! 

 Thus in 1871 the Slieuncater expedition, under Captain 

 Nares and Dr. Carpenter, found a bottom temperature at | 

 1650 fathoms of 56°, and the year previous the same 

 temperature had been met with at a spot where the sea 

 bed was 1713 fathoms from the surface. In 1881, how- 

 ever, Captain I\Iagnaghi, Hydrographer to the Italian 

 Navy, along with Professor Giglioli, in the surveying 

 vessel Waxliiniiton, found the bottom temperature to be 

 1° higher than that recorded as the mean of those ob- 

 tained in 1871. The mean temperature of the months of 

 December, -January, February, March, and April is 53-6° F. 

 at Toulon and 56'81° F. at Algiers, and the average of these 

 two temperatures gives approximately the degree of heat 

 contained in the Mediterranean Sea bed between those two 

 places. 



With regard to the Adriatic Sea, soimdings show that 

 only one-third of its area can be regarded as forming a 

 part of the Mediterranean basin proper, the remaining 

 portion not averaging more than 50 fathoms in depth. A 

 channel of 100 fathoms stretches across the entrance to 

 the sea, from Otranto to Albania. Within the sea the 

 depth increases until a maximum of 705 fathoms is attained, 

 and this rapidly shoals until the comparatively shallow 

 waters of the northern portion of the sea are encountered. 

 The PiA<i made some interesting experiments relative to the 

 transparency of the Mediterranean waters, In three cases 

 a white disc was seen down to a depth of 177 feet. Where 

 the water was deepest, however, invisibility was reached 

 at 105 feet. 



The paucity of animal life in the great depths of the 

 Mediterranean is well known. Its depths are to a certain 

 extent stagnant. There is an utter absence of that vertical 

 circulation so thoroughly developed in the Atlaniic, and 

 which results in process of time in every particle of water 

 being alternately transposed from sea bed to surface, and 

 surface to sea floor. The only semblance of such a circu- 

 lation that exists in the Mediterranean is caused by the 

 descent of water that has been concentrated by evaporation 

 on the surface, and has thus had its specific gravity raised 

 above that of tlie underlying strata. But tiie descent of 

 this water will be seriously interfered with at a depth of 

 .200 or 300 fathoms, where the temperature is such that 

 it will encounter an aqueous layer whose specific gravity 

 is much akin to its own. 



It will be remembered that it was owing to the absence 

 of life met with during the researches of Professor E. 

 Forbes, in the .Egean Sea, that the erroneous doctrine 

 was formulated that marine oceanic life ceased at a depth 

 of about 300 fathoms. 



Subsequent explorations in the deep sea speedily showed 

 the fallacious character of such a conclusion, except in 

 enclosed seas of the Mediterranean type. 



In the western basin of the Mediterranean, the bottom 

 consists chiefly of clay, of a grey or brownish colour. It 

 always contains some carbonate of lime, the remains of 

 foraminifera. Both in appearance and chemical constitution 

 the mud resembles that dredged up in the open ocean from 

 areas which are shut off by submarine ridges from free 

 participation in the vertical oceanic circulation. 



In the eastern section of the Mediterranean the sea bed 

 deposits contain a considerable proportion of volcanic ash 

 and other constituents of igneous origin. 



Before proceeding to discuss the character of the 

 connecting channels and currents that unite the Mediter- 

 ranean Sea with the Atlantic Ocean and the Black Sea, wc 

 will briefly allude to the liudiugs of the latest researches 

 conducted" in the waters of the last named sea. 



The Russian gun-boat the Tchernoiitoret; was engaged in 

 Juns and July, 1890, in the work of surveying. The 

 maximum depth, 7305 feet, was found in the central 

 portion of the sea, between the Crimea and Anatolia. 

 The explorations were continued last year, and the results 

 of the previous year's work were confirmed. The 100 

 fathoms lino was found to lie close to the shores of the 

 Crimea and Anatolia, and the axis of greatest depression 

 has a direction from sonth-west to north-east. The 

 steepest coast was found at Piizo, where the angle of 

 inclination attains 10". The most interesting of the 

 recorded observations are those relating to the temperature 

 of the Black Sea waters. The variations of temperature 

 at the surface range from 77° F. to 11° F., while on the 

 northern shores the thermometer sometimes falls below 

 the freezing point. The annual variations of temperature, 

 due to the seasons, do not penetrate deeper than 100 

 fathoms. At a depth of from 30 to 175 feet the 

 temperature was 57° towards the south coast, 51° in the 

 centre, and 52° near the east, west, and north shores. 



The water begins to be warmed by the air in the month 

 of May, and during August the mean temperature of the 

 surface water is higher than that of the superincumbent 

 air. The variation of temperature for depths below 180 

 feet is very peculiar. At this point the thermometer 

 registers 15° F. Then the thermometer begins to rise, 

 and at a depth of 6000 feet it shows 49" F. For all depths 

 below 200 fathoms the temperature may be described as 

 constant, and lying between 19° F. and 18° F. The most 

 distinctive feature of the Black Sea, however, is that at the 

 depth of 450 feet distinct traces of sulphuretted hydrogen 

 occur. The quantity increases with the depth, until at 

 600 feet it is quite sensible, and at the mean depth of 940 

 feet it renders animal life quite impossible. Some even 

 place the inferior limit of organic lite at so high a level as 

 100 fathoms. Dredgings show that at one period of 

 geological history the Black Sea contained an abundance 

 of low organisms, and the semi -fossil shells of certain 

 molluscs characteristic of the brackish water of the lagoons 

 of the Caspian and Black Seas are much m eridencc. 

 These fossils are doubtless the remains of the Pontic fauna 

 of the Pliocene period, when the Black Sea basin was not 

 connected with the Mediterranean. The salinity of the 

 Black Sea was then by no means so great as it is now. 

 When the connection between the two seas was made, the 

 water from the Mediterranean would make its way as it 

 does at present into the Black Sea area, and speedily lead 

 to the disappearance of the ancient fauna. Thus the 

 sulphuretted hydrogen is one of the products formed by the 

 decomposition of the older life, and as the water in the 

 great depths is practically stagnant, I.e., quite motionless, 

 it follows that the decay is an exceedingly slow process. 



Assuming that the water which annually flows through 

 the Bosphorus into the Black Sea forms a one-thousandth 

 part of the total contents of the sea, it will take 1000 years 

 to completely renew the whole contents of the basin. It 

 will be thus easily seen to what small extent the deep 

 waters participate in the scheme of circulation. The Sea 

 ■ of Azov is merely the expanded mouth of the River Don, 

 its waters being shallow, having no greater depth than 7^ 

 fathoms, and being thoroughly mixed by each storm that 

 ' visits it. 



The Sea of Azov, too, shares in the disturbing influences 

 I of the surface current which sweeps round the shores of 



