6 PHYSICAL GEOGRAPHY OF THE SEA. 



the eye by their monotonous uniformity ; on others, where these 

 natural bulwarks are wanting, artificial embankments, or dykes 

 protect the lowlands against the encroachments of the sea, or else 

 the latter forms vast salt-marshes and lagunes. On some coasts 

 these submerged or half-drowned lands have been transformed 

 by the industry of man into fertile meadows and fields, of which 

 the Dutch Netherlands afford the most celebrated example ; while 

 in other countries, such as Egypt, large tracts of land once cul- 

 tivated have been lost to the sea, in consequence of long misrule 

 and tyranny. 



How deep is the sea ? How is its bottom formed ? Does 

 life still exist in its abyssal depths ? These mysteries of ocean, 

 which no doubt floated indistinctly before the mind of many an 

 inquisitive mariner and philosopher of ancient times, have only 

 recently been subjected to a more accurate investigation. Their 

 solution is of the highest importance, both to the physical 

 geographer, whose knowledge must necessarily remain incom- 

 plete until he can fully trace the deep-sea path of oceanic 

 currents, and to the zoologist, to whom it affords a wider in- 

 sight into the laws which govern the development of the 

 innumerable forms of life with which our globe is peopled. 



The ordinary system of sounding by means of a weight at- 

 tached to a graduated line, and " armed " at its lower end with 

 a thick coating of soft tallow, so as to bring up evidence of its 

 having reached the bottom in a sample of mud, shells, sand, 

 gravel, or ooze, answers perfectly well for comparatively shallow 

 water, and for the ordinary purposes of navigation, but it 

 oreaks down for depths much over 1000 fathoms. The weight 

 is not sufficient to carry the line rapidly and vertically to the 

 bottom; and if a heavier weight be used, ordinary sounding 

 line is unable to draw up its own weight along with that of the 

 lead from great depths, and gives way, so that by this means no 

 information can be gained as to the nature of the sea-bottom. 

 To obviate this difficulty, several ingenious instruments have 

 been invented, such as the " Bull-dog " sounding machine, which 

 is so contrived that on touching the bottom the weight becom s 

 detached, while at the same time a pair of scoops, closing upon 

 one another scissorwise on a hinge, and permanently attached 



