DEPOSITS OF THE ATLANTIC IN DEEP WATER, ETC. 27 
the east, runs between and past the Faroe islands and the bank 
called Eockall ; while a third cold current passes along the 
coast of Scotland. All these are in comparatively shallow water, 
rarely exceeding 1,000 fathoms, and all are strictly limited by 
natural barriers. 
It is not to be supposed that there can be this continual 
drain of cold water from the arctic seas without some supply 
being drifted in by counter currents. No doubt there is a very 
large and constant evaporation from the mid- Atlantic, but there 
is also a heavy rainfall and a large number of streams pouring 
into the ocean the drainage both of Europe and America. 
There are in fact two deep warm currents, one between Iceland 
and the Rockall and Faroe banks, and the other between these 
banks and Scotland both also shut in by natural barriers.* 
These warm currents proceed from a deep central warm tract of 
ocean tying to the east and north-east of the limit of the Gulf 
Stream, and it is this warm tract, with its branches northwards, 
that affords in its floor the conditions apparently most favour- 
able for certain deposits that have lately been described as 
resembling chalk. 
The deep sea explorations of late years carried on with im- 
proved means of determining bottom temperature, have made 
it clear that there are well marked deep areas that possess 
a warm temperature, not very far from other areas where the 
bottom temperature is uniformly low. It is a further result of 
the same work that over the cold areas generally the bottom is 
sandy, often of volcanic sand, and these parts exhibit a con- 
siderable variety and sometimes a great wealth of animal life; 
but the organic forms but a small proportion in comparison to 
the inorganic element. Here, however, a vast multitude of the 
curious worm-like marine animals assuming a coat of agglu- 
tinated grains of sand have been met, and the multitude of 
new species obtained in recent soundings is so great that there 
is a difficulty in finding names for them. Besides annelids, 
sponges, echinoderms, mollusks, and crustaceans have been 
found, so that these regions are, on the whole, exceedingly rich. 
In one spot alone where the dredge brought up but little, a 
tangle of hemp lifted at one haul many thousand specimens of 
a single form of echinus. 
On the other hand, in the warmer areas the deposit of mud 
consisted exclusively of a peculiar material called ooze or oaze 
* It was found in tlie recent (1869) expedition that a difference in bottom 
temperature, between 32° and 47°, existed at points only eight or ten miles 
distant beneath a uniform surface temperature of about 52°. In such cases 
the cold area was paved with barren sandstone having a scanty boreal fauna, 
while in the adjacent warm area the bottom was mud, with an abundant 
temperate fauna. 
