ON A PIECE OF CHALK 59 



enough. It is a discovery which, like others of no less scien- 

 tific importance, has arisen, incidentally, out of work devoted 

 to very different and exceedingly practical interests. 



When men first took to the sea, they speedily learned to 

 look out for shoals and rocks ; and the more the burthen of 5 

 their ships increased, the more imperatively necessary it 

 became for sailors to ascertain with precision the depths of 

 the waters they traversed. Out of this necessity grew the 

 use of the lead and sounding line ; and, ultimately, marine- 

 surveying, which is the recording of the form of coasts and of 10 

 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. 15 

 Some ingenious tar, whose name deserves a better fate than 

 the oblivion into which it has fallen, attained this object by 

 "arming" 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. 20 

 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 25 

 most ingenious machine, by which a considerable 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, 30 

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

 of this sounding apparatus. The specimens were sent for 

 examination to Ehrenberg of Berlin, and to Bailey of West 

 Point, and those able microscopists found that this deep-sea 



