uf Edinburgh, Session 1883-84. 
517 
waters tlie tempGi\atiire ranges from 80° T'alir. in the tropics, to 28° 
Fahr. in the polar regions. Below the surface, down to the nearly ice- 
cold water found at the lower limits of the region in the deep sea, 
there is in the tropics an equally great range of temperature. Plants 
and animals are abundant near the shore, and animals extend in 
relatively great abundance down to the lower limits of this region 
which is now covered by these terrigenous deposits. The specific 
gravity of the water varies much, owing to mixture with river water 
or great local evaporation, and this variation in its turn affects 
the fauna and flora. In the terrigenous region tides and currents 
produce their maximum effect, and these influences can in some 
instances be traced to a depth of 300 fathoms, or nearly 2000 feet. 
The upper or continental margin of the region is clearly defined by 
the bigh-water mark of the coast-line, which is constantly changing 
through breaker action, elevation, and subsidence. The lower or 
abysmal margin is less clearly marked out. It passes in most cases 
insensibly into the abysmal region, but may be regarded as ending 
when the mineral particles from the neighbouring continents begin 
to disappear from the deposits, which then pass into an organic ooze 
dr a red clay. 
Contrast with these those conditions which prevail in the 
abysmal region in which occur the organic oozes and red clay, 
the distribution of which will presently be considered. This area 
comprises vast undulating plains from two to five miles beneath 
the surface of the sea, the average being about three miles, here 
and there interrupted by huge volcanic cones (the oceanic islands). 
No sunlight ever reaches these deep cold tracts. The range of 
temperature over them is not more than 7°, viz., from 31° to 38° 
Fahr., and is apparently constant throughout the whole year in each 
locality. Plant life is absent, and although animals belonging to 
all the great types are present, there is no great variety of form 
or abundance of individuals. Change of any kind is exceedingly 
slow. 
What is the distribution of deposits in this abysmal region 
of the earth’s surface ? In the tropical and temperate zones 
of the great oceans, which occupy about 110° of latitude between 
the two polar zones, at depths where the action of the waves is not 
felt, and at points to which the terrigenous materials do not extend, 
