DEPTH OF THE OCEAN. 7 



Dr. Maury has constructed his fine orographic map of the basin of 

 the Atlantic. Dr. Maury has also pubhshed many charts, giving the 

 depths of the ocean, the substance of which is given in the accom- 

 panying map, which represents the configuration of the Atlantic up 

 to the tenth degree of south latitude, not in figures, as in Dr. Maury's 

 charts, but in tints ; diagonal lines from right to left, representing the 

 shores of both hemispheres, indicate a depth of less than i,ooo 

 fathoms ; from left to right indicate bottom at i,ooo to 2,000 ; hori- 

 zontal lines, 2,000 to 3,000 fathoms ; cross lines show an average 

 depth of 3,000 to 4,000 fathoms ; finally, the perpendicular hues in- 

 dicate a depth of 4,000 fathoms and upwards. Solid black indicates 

 continents and islands ; waving lines, surrounding both continents at 

 a short distance from the shore, indicate the sands which surround 

 the coast line at a little distance from the shore. 



The question may be asked, what useful purpose is served by 

 taking soundings at great depths ? To this we may quote the 

 answer of Franklin to a question of similar tendency, addressed to 

 aeronauts — "What purpose is served by the birth of a child?" 

 Every fact in physics is interesting in itself; it forms a rallying point, 

 round which, sooner or later, others will meet, in order to estabhsh 

 some useful truth ; and the importance of making and recording 

 deep-sea soundings is established by the successful immersion of the 

 transatlantic telegraph. 



At the bottom of the Atlantic there exists a remarkable plateau, 

 extending from Cape Race in Newfoundland, to Cape Clear in 

 Ireland, a distance of over 2,000 miles, with a breadth of 470 miles ; 

 its mean depth along the whole route is estimated at two miles and a 

 half. It is upon this telegraphic plateau, as it has been called, that 

 the attempt was made to lay down the cable in 1858, and it is 

 on it that the enterprise was so successfully completed during the 

 year 1866. The surface of the plateau had been previously explored 

 by means of Brooke's apparatus, and the bottom was found to be 

 composed chiefly of microscopic calcareous shells {Foraminifera), 

 and a few siliceous shells [Diatoviacece). These delicate and fragile 

 shells, which seemed to strew the bottom of the sea in beds of great 

 thickness, were brought up by the sounding-rod in a state of perfect 

 preservation, which proves that the water is remarkably quiet in 

 these depths — an inference which is fully borne out by the condition 

 in which the cable of 1858 was found, when picked up in 1866. 



The first exploration of this plateau was undertaken by the 

 American brig Dolphin, which took 100 soundings 100 miles from 



