352 



GEOGRAPHICAL PROGRESS AND DISCOVERY. 



ity, parallel to the axes of the adjoining con- 

 tinents. The soil in the bed of the ocean con- 

 sists, for 300 or 400 miles from the shores, of 

 sedimentary deposits of material derived from 

 the detrition of the shore rocks. Down to 2,- 

 000 fathoms depth the globigerina ooze, com- 

 posed of the shells of foraminifera living on the 

 surface of the water, forms the bottom. Be- 

 yond 2,500 or 3,000 fathoms these shells are 

 decomposed as they sink by the carbonic acid 

 in the water. Below such depths the bottom 

 is an extremely fine reddish clay, composed in 

 part of the shells of radiolarians and in part of 

 Hakes of pumice and crystalline fragments of 

 volcanic minerals ; the residue is made up of 

 decomposed volcanic matter and the mineral 

 constituents of organisms. Nodules are found 

 in great numbers, formed by concentric layers 

 of peroxide of iron and peroxide of manganese, 

 deposited in a matrix of clay around a nucleus, 

 which is a shark's tooth, a piece of bone or si- 

 licious sponge, a fragment of pumice, or other 

 hard substance. Particles of magnetic iron 

 and magnetic nickel of doubtful origin are dis- 

 tributed through the red bottom soil. The red 

 bottom is nothing like any previous geological 

 formation, so that it appears that no previous 

 sedimentary formation was deposited at such 

 great depths. 



Sir Wyville Thomson added a resume of the 

 knowledge attained of the antarctic regions and 

 the inferences concerning them derived from 

 the better understanding lately acquired of the 

 ocean circulation and the nature of ice forma- 

 tions. The unexplored region beyond the 70th 

 parallel south of the equator, comprising an 

 area of 4,700,000 square miles, is quite likely 

 not a continuous antarctic continent, but a 

 congeries of low continental land and of con- 

 tinental islands connected together by bridges 

 of ice, which form part of a solid ice-cap cov- 

 ering the whole to the height of about 1,400 

 feet. The region is transsected by continental 

 chains, like the range between 55 and 95, 

 which includes Peter the Great Island and Al- 

 exandra Land, Graham Land and Adelaide Isl- 

 and, and Louis Philippe Land, and by at least 

 one volcanic range, discovered by Ross in 1841, 

 which stretches from Balleny Island to lat. 78 

 8., and attains an altitude of 15,000 feet. The 

 antarctic lands are surrounded by a fringe of 

 ice which ends in a perpendicular cliff of an 

 average height of 230 feet, outside of which a 

 floe extends seaward in winter, 20 feet thick or 

 more, and in summer the floe gives place to 

 drifting pack-ice and icebergs. Sir Wyville 

 propounded a theory to explain why the sheet 

 of ice which covers the antarctic region does 

 not indefinitely increase in thickness, but main- 

 tains a uniform depth of 1,400 feet, which is 

 the height of the southern icebergs. These, 

 from their stratification and snowy tops are 

 evidently prismatic blocks fallen from the edge 

 of the great cap of antarctic ice as it protrudes 

 over the sea; this is shown also from the fact 

 that the bottom of the ocean in the zone where 



the icebergs begin to melt is covered with peb- 

 bles and other land detritus. The stratification 

 of the ice in the bergs is horizontal, and the 

 strata diminish in thickness uniformly down- 

 ward. The top layers, 60 or 80 feet below the 

 snow-clad top, is a foot thick and whitish, indi- 

 cating the presence of air ; but it is hard, and 

 has a specific gravity little less than that of 

 the strata at the water-line, which are only 

 three inches thick. It seems certain that the 

 diminished thickness of the lower strata is due 

 not alone to compression, but also to the loss 

 of some of their substance. It is probable that 

 at the lower part of the glacial sheet, where 

 the pressure at the depth of 1,400 feet is 500 

 pounds to the square inch, a process of melt- 

 ing takes place, the water passing down by 

 gravitation from layer to layer, and finally es- 

 caping below the bottom of the ice-sheet. It 

 is probable from the uniform thickness of the 

 crust covering the antarctic region and the 

 above-described indications that, at the temper- 

 ature of the earth's crust at the bottom of the 

 antarctic ice-sheet, the body of ice can not be 

 maintained of a greater thickness than 1,400 

 feet with melting from the pressure and the in- 

 ternal heat of the earth. 



A new English expedition for deep-sea ex- 

 ploration has departed under Sir George Nares. 

 The Alert, on board of which vessel the sur- 

 veys and scientific investigations are to be 

 made, has been refitted and provided for a cir- 

 cumnavigatory voyage of great magnitude. 

 Twelve officers and one hundred and twelve 

 men shipped in her from Portsmouth for a 

 three years' cruise. The first task will be a 

 much-needed survey of the dangerous Straits 

 of Magellan. The numerous islets in the straits 

 will be explored, and a triangulation of the 

 entire waters between Terra del Fuego and the 

 mainland and along the coast of Patagonia 

 will be taken, with a complete series of sound- 

 ings, and a chart prepared which will greatly 

 shorten the voyage into the Pacific. The next 

 task will be the exploration of the unvisited 

 isles and coral reefs of the Pacific, particularly 

 those east of the Society Islands,- between the 

 135th and 149th degrees. The variations in 

 the depth of the ocean from volcanic action 

 near the Feejee Islands will be studied. Then 

 soundings will be taken in Torres Strait, along 

 the west coast of Australia, in Geography Bay 

 and King George Strait, where the expedition 

 will terminate, and return to Portsmouth by 

 way of Suez. 



The next serious attempt to pierce the arcana 

 of the arctic regions will probably be made by 

 way of the Barentz Sea and along the coast of 

 Nova Zembla and Franz Joseph Land. It is 

 expected that the Discovery, a steamer of great 

 power and fitted for sailing through the ice, 

 may be sent out from England on such an ex- 

 pedition in the summer of 1879. The knowl- 

 edge of the movements of the ice in those seas 

 has been considerably enriched by the expe- 

 rience gained in two cruises made this last 



