80 New York State Museum 



100- fathom line, the depth to which effective sunlight 

 penetrates, which is also the limit of green plant life. This 

 realm, besides being characterized by the presence of 

 light, is also marked by the absence of a substratum. It 

 has been regarded as the seaward extension of the flach- 

 see, and is a zone of swimming and floating forms. 



The abyssal realm (Greek abyssos, bottomless) includes 

 that portion of the sea beyond the continental shelf and 

 beneath the pelagic zone, that is, below the 100- fathom 

 line. This realm has been divided into two zones : the 

 zone of swimming and floating organisms where there is 

 no substratum, the abysso-pelagic zone; and the zone 

 where there is a bottom present or the abysso-benthonic 

 zone. The abyssal zone is characterized by an absence 

 of light, absence of motion, except for the extremely slow 

 progress of sluggish ocean currents, and cold and great 

 pressure. In the upper transitional layers of the abys- 

 sal realm there is some light but it has not the essen- 

 tials necessary to the existence of plant life. The 

 animals in this zone therefore must all be carnivorous 

 or feed upon dead organic matter. In all the oceans 

 below a certain depth the waters are permanently cold 

 and have a temperature nearly at the freezing point of 

 fresh water. Pressure in the deeps is enormous since 

 pressure increases directly with the depth at the rate 

 of about one ton to a square inch for every thousand 

 fathoms of depth. All these things mean that the 

 abyssal realm is an area of vast extent and constitutes 

 an environment that is simple and of a comparatively 

 uniform and changeless nature. There is correspond- 

 ing response in the life of this realm. 



