LIFE. 611 



zones of surface-temperature see the Physiographic Chart, and pages 

 12-44. 



As already explained, the temperature of the ocean is greatly influ- 

 enced by the currents ; and while tropical currents carry warm waters 

 pole-ward, along certain courses determined by the outline of the 

 oceanic basins, the cold polar currents sweep equator-ward over the 

 ocean's broad bottom, nearing the surface chiefly on the west side of 

 the ocean. 



The deep-sea temperature at the ocean's bottom is generally about 35° F., and in 

 parts of the polar seas and the courses of polar currents, as low as 28° F. But 40° to 45° 

 F. is usually found in the tropics within 300 fathoms of the surface; and as low as 40° 

 F. almost everywhere under 1300 fathoms. The bottom of the Atlantic along the mar- 

 gin of the basin washed by the Gulf Stream, between 60 and 150 fathoms in depth, 

 and at 600 to 800 fathoms in British seas, where the temperature is mostly above 55°, 

 literally swarms with life (A. Agassiz, Verrill, "Wyville Thomson); and in greater and 

 colder depths the species are little less abundant. Fishes, Crabs, and other Crustaceans, 

 Echini, Star-rishes, Crinoids. Corals, sea Worms, some of the kinds of extraordinary size, 

 occur to a depth of 10,000 to 13,000 feet, and many species are living at nearly 18,000 

 feet, and probably beyond. But the species within the sweep of the warm current differ 

 to a great extent from those in the colder waters, so that there is a warmer-water and a 

 colder-water section among the deep-sea species. 



The Rhizopod shells or Foraminifers of the Globigerina ooze, and the Diatoms of 

 siliceous deposits, are believed to have dropped to the bottom from near the surface, the 

 living species, although pelagic, being confined to shallow depths. 



Again, there are species that grow in waters above the ordinary temperature. Some 

 of the simpler Algae, and especially microscopic species, will grow in waters even hot. 



At the Hot Springs ("Geysers"), on Pluton Creek, California, Prof. Wm. H. 

 Brewer observed Conferva?, in waters heated to 140°-149 D F., and simpler Alga? where 

 the temperature was 200° F. At the same place, Dr. James Blake found two kinds of 

 Conferva?, in a spring of the temperature of Vd^, and many Oscillatoriw and two 

 Diatoms, in one of 174°. In the waters of Pluton Creek, of 112° F., the Alga? formed 

 layers three inches thick. Dr. Blake also collected fifty species of Diatoms, from a 

 spring in Pueblo Valley, Nevada, the temperature being 163° F. ; and they were mostly 

 identical with those of beds of infusorial earth in Utah. 



The various hot springs of the several Geyser Basins, in the Yellowstone National 

 Park, contain very various Confervoid forms. The hottest springs, up to 200° F., 

 contain numerous, long, slender, white and yellow vegetable fibres, on undetermined 

 relations, waving in the boiling eddies, and becoming buried in the siliceous deposits 

 over the bottom, where they often form layers several inches thick. The bright green 

 forms appear to be confined to lower temperatures. W. R. Taggart reports that, at 

 the vents on the shores of Lewis's Lake, leajy vegetation is limited to temperatures 

 below 120° (Ilaydeivs Reports, 1871-2). Dr. Josiah Curtis found, in these hot springs, 

 siliceous skeletons of very numerous Diatoms; but the vegetable matter was wanting, 

 in all cases, where the temperature exceeded 96° F. So many different causes might 

 introduce these skeletons to the hotter pools, that their presence has not necessarily 

 any more significance than that of the grasshoppers and butterflies which are frequently 

 found in the same pools. Living larves of Helicopsyche were found, by Mr. Taggart, 

 in a spring having the temperature of 180°, into which, however, they might have 

 crawled from the river, which was close by; so that the eggs were not necessarily laid 

 at the temperature given. 



At Bafios, on Luzon, Phillipine Islands, the author observed feathery Conferva?, in 

 waters heated to 160° F. 



