XVI.] FORAMINIFERAL LAND. 263 



into another; and thus several may be fitted together, 

 forming a compact mass perforated by a central canal, 

 through which the tube passes. As the instrument runs 

 down, water enters the tube a, at its open end e, and passes 

 out through holes in the ' upper part. On striking the 

 bottom, the tube sinks into the mud or other material, and 

 a small quantity enters ; and this is prevented from escaping 

 by means of a pair of butterfly-valves, opening inwards, 

 which are attached to the bottom, e. When the floor of the 

 sea is touched, the brass cylinder, b, is pushed up, and 

 striking the shoulder, c, of the iron piston, throws off the 

 sling, and thus releases the weight. Thus, when the line to 

 which the instrument is attached is hauled in, it comes to 

 the surface, carrying nothing but the tube full of the sea- 

 bottom. It is by means of such instruments that the deep 

 sea has been sounded, and samples of the bottom brought 

 to the surface for scientific examination. 



The careful soundings made during these surveys revealed 

 the remarkable configuration of the Atlantic sea-bed. This 

 is shown in Fig. 78, which shows the contour of the floor of 

 the sea between Valentia Island off Ireland, and St. John's in 

 Newfoundland. It will be seen that there is a gradual down- 

 ward slope from the Irish coast, for a distance of about 200 

 miles ; then there is a more rapid descent ^ leading to a vast 

 undulating plain which stretches across the ocean, until it 

 reaches a distance of about 300 miles from Newfoundland, 

 and from thence it gradually ascends towards the American 

 coast. This great submarine plain, wliich has been called the 



1 In the diagram this descent looks like a steep cliff. But this is a 

 deception arising from the exaggeration of the vertical height. Drawn 

 to a true scale as in D, Fig. 78, the inclination of the slope is seen to 

 be not more than l in 25, or that of a hill of moderate steepness. If 

 it were a mere question of gradients, a waggon could be driven along 

 the sea-bottom from Ireland to Newfoundland without any difficulty. 



