ix.J ON A PIECE OF CHALK. 157 



recording of the form of coasts and of the depth of the sea, as 

 ascertained by the sounding-lead, upon charts. 



At the same time, it became desirable to ascertain and to 

 indicate the nature of the sea-bottom, since this circumstance 

 greatly affects its goodness as holding ground for anchors. Some 

 ingenious tar, whose name deserves a better fate than the 

 oblivion into which it has fallen, attained this object by &quot; arming &quot; 

 the bottom of the lead with a lump of grease, to which more or 

 less of the sand or mud, or broken shells, as the case might be, 

 adhered, and was brought to the surface. But, however well 

 adapted such an apparatus might be for rough nautical purposes, 

 scientific accuracy could not be expected from the armed lead, 

 and to remedy its defects (especially when applied to sounding 

 in great depths) Lieut. Brooke, of the American Navy, some 

 years ago invented a most ingenious machine, by which a con 

 siderable portion of the superficial layer of the sea-bottom can 

 be scooped out and brought up, from any depth to which the 

 lead descends. 



In 1853, Lieut. Brooke obtained mud from the bottom of the 

 North Atlantic, between Newfoundland and the Azores, at a 

 depth of more than 10,000 feet, or two miles, by the help of 

 this sounding apparatus. The specimens were sent for ex 

 amination to Ehrenberg of Berlin, and to Bailey of West Point, 

 and those able microscopists found that this deep-sea mud was 

 almost entirely composed of the skeletons of living organisms 

 the greater proportion of these being just like the Globigerince 

 already known to occur in the chalk. 



Thus far, the work had been carried on simply in the interests 

 of science, but Lieut. Brooke s method of sounding acquired a 

 high commercial value, when the enterprise of laying down the 

 telegraph-cable between this country and the United States was 

 undertaken. For it became a matter of immense importance to 

 know, not only the depth of the sea over the whole line along 

 which the cable was to be laid, but the exact nature of the 

 bottom, so as to guard against chances of cutting or fraying the 

 strands of that costly rope. The Admiralty consequently 



