B 



TRAXSACTIONS OF THE SECTIONS. 173 



In the Atlantic Oceau, from a high southern latitude a broad channel, with not 

 less than some 12,000 to 15,000 feet, can be traced as extending nearly to the 

 entrance of Davis Strait ; a dividing undulating ridge of far less depression, on 

 which stand the islands of Tristan d'Acunha, St. Helena and Ascension, separates 

 this, which may be named the western channel, from a similar one running parallel 

 to the South- African continent, and which extends to the parallel of the British 

 Islands. It is possible that certain tidal and, indeed, climatic conditions peculiar 

 to the shores of the North Atlantic may be traced to this bottom conformation, 

 which carries its deep, canal-like character into Davis Strait, and between Green- 

 land, Iceland, and Spitzbergen, certainly to the 80th parallel. 



There is, however, one great feature common to all oceans, and which may have 

 some significance in the consideration of ocean circulation, and as affecting the 

 genesis aud translation of the great tidal wave and other tidal phenomena, of 

 which we know so little — namely, that the fringe of the seaboard of the gTeat con- 

 tinents and islands, from the depth of a few huncbed feet below the sea-level, is, 

 as a rule, abruptly precipitous to depths of 10,000 and 12,000 feet. This grand 

 escarpment is typicall}^ illustrated at the entrance of the Eritish Channel, where 

 the distance between a depth of 600 feet and 12,000 feet is in places only ten 

 miles. Imagination can scarcely realize the stupendous marginal featm-es of this 

 common siirface-depression. 



Vast in extent as are these depressed regions— for we must recollect that they 

 occupy an area three times as gTeat as the dry land of the globe, and that a 

 temperatm-e just above the freezing-point of Fahrenheit prevails in the dense liquid 

 layers covering them — life is sustained even in the most depressed and coldest 

 parts ; while in those areas equivalent in depression below the sea-level to the ele- 

 vation of European Alpine regions above it animal life abundantly prevails ; structural 

 forms complicated in arrangement, elegant in appearance, and often lively in colour 

 clothe extensive districts ; other regions apparently form the sepulchral resting- 

 place of organisms which when living existed near the surface, their skeletons, as 

 it has been gi'aphically put, thus "raining down in one continuous shower through 

 the intervening miles of sea water." Geological formations, stamped with the 

 permanency of ages, common to us denizens of the dry land, appear, too, in these 

 regions to be in course of evolution ; forces involving the formation of mineral 

 concretions on a grand scale are at work ; life is abundant everywhere in the sur- 

 face and sub-surface waters of the oceans ; in fine, life and death, reproduction and 

 decay, are active in whatever depths have been attained. 



As a question of surpassing interest in the great scheme of nature, the economy 

 of Ocean Circulation, atiecting as it does the climatic conditions of countries, has 

 of late attracted attention. The general facts of this circulation in relation to 

 climate have been thus tersely summarized : " Cold climates follow polar waters 

 towards the equator ; warm climates fullow warm equatorial streams towards the 

 poles." We can all appreciate the geniality of our own climate, eepecially on the 

 western shores of the kingdom, as compared with the Arctic climate of the shores 

 of Labrador, situated on the same parallels of latitude, or indeed with the vigorous 

 winter climate of the adjacent North- American seaboard, even ten degrees further 

 to the south. These, and liindred features in other parts of tlie globe, have led to 

 the summarized generalization I have just referred to; but the iHitionale of these 

 movements of the waters is by no means assured to us. 



That ocean currents were due primarily to the trade and other prevailing winds, 

 was the received opinion from the earliest investigation made by navigators of the 

 constant surface-movement of the sea. Rennell's views are thus clearlj'' stated : — 

 " The winds are to be regarded as the prime movers of the currents of the ocean ; 

 and of this agency the trade-winds and monsoons ha^e by far the greatest share, 

 not only in operating on the larger half of the whole extent of the circumambient 

 ocean, iDut as possessing greater power by their constancy and elevation to generate 

 and perpetuate currents;" . . . " next to these, in degree, are the most pre- 

 valent winds, such as the westerly winds beyond, or to the north and south of, the 

 region of trade winds." 



Mauiy, so far as I am aware, was the first to record his dissent from these 

 generally received views of surface-currents being due to the impulse of tha winds, 

 ^ 1876. 16 



