QUEKETT MICROSCOPICAL CLUB. 337 



or free-swimmers ; and (3) Plankton, or drifters. The last section, 

 which consists largely of algae and protista, is the most important. 

 The plankton lives principally in the surface water to the depth 

 where light ceases, but dies in the mid-waters of the ocean. 

 The problem of the distribution of plankton has been solved by 

 the use of the tow-net. Mr. Earland showed samples of tow- 

 nettings taken under various conditions of depth, etc., and 

 described the nets used by means of diagrams on the screen. 



Mr. Earland then described how the depth of the sea increases 

 as the distance from the land, making special reference to the 

 North Sea. The bottom slopes gradually away from the shore- 

 line to a depth of about 100 fathoms and until it reaches the 

 edge of the " Continental shelf," which marks the original shore- 

 line of the ancient continent before denudation of the earth's 

 surface began to raise the surface of the seas. Hereabouts lies 

 Murray's " mud line," at which limit the finest material denuded 

 from the land comes to settlement, furnishing an abundant supply 

 of food to the varied forms of marine life which congregate about 

 this depth. At Murray's line such forms as foraminifera are 

 found at their best. No purely terrigenous deposits occur outside 

 the Continental shelf, which in this corner of Europe lies to the 

 north of the Shetland Islands. From the Continental shelf the 

 " Continental slope " drops sharply down to the " abyssal plain." 

 To oceanographers any part of the ocean beyond 3,000 fathoms 

 is known as a " deep." The North Sea, no part of which is 

 deep enough entirely to submerge St. Paul's Cathedral, is shallow 

 water. The deepest sounding so far discovered in the ocean is 

 in the " Swire " deep, off the Philippine Islands, 5,364 fathoms — 

 nearly a mile deeper than Mount Everest is high. The pressure 

 at such a depth is 960 atmospheres, or 6-4 tons to the square 

 inch. The organisms that live at great depths in the sea are 

 not affected by the pressure so long as they remain at about the 

 same depth. If they are brought up to the surface the results 

 are disastrous, fishes being burst open or their internal organs 

 forced out by the great alteration in pressure. The speaker had 

 seen a fir pole that had been sent down to 1,000 fathoms come 

 up swollen to double its original size, owing to the compression 

 and subsequent expansion of its cellular tissues. An iron socket 

 which had been tightly fitted on to its end had fallen ofi during 

 its descent owing to the compression of the wood. 



