LIFE. 611 



when the polar and tropical are alongside, as in some parts of the 

 North Atlantic, cold-water and warm-water species are living within 

 a short distance of one another. Some species have a wide range of 

 favorable temperature, and others a very narrow range. 



The zones of oceanic temperature are marked on the Physiographic 

 Chart, and are explained on pages 42 to 44, where also facts are men- 

 tioned illustrating the geological bearing of the subject. 



The following zones in depth have been recognized by Forbes and other observers, 

 for the convenience of marking the distribution of marine species: — 



1. The Littoral zone, — or the tract between high-tide and low-tide levels. 



2. The Laminarian zone, — from low water to fifteen fathoms (90 feet). This zone 

 is so named from the fucoidal sea-weed, called sometimes Tangle-weed, which is of 

 the genus Laminaria, a plant especially of rocky shores. 



3. The Coralline zone, — from 15 to about 50 fathoms. 



4. The Deep-sea Coral zone, — from 50 to 300 fathoms. 



5. Abyssal zone, — below 300 fathoms, the ocean abounding in life down to a depth of 

 2,500 fathoms. 



But the recent observation that the same species that live in shallow water at the 

 north may continue along the corresponding zone of temperature at various depths 

 down to many hundred fathoms, has lessened the importance attached to these zones, 

 and especially to the two lower. For example, the Rhizocrinus Lofotensis Sars, and 

 over thirty species of other invertebrates, including corals, occur in the vicinity of the 

 Lofoten Islands, in the Scandinavian seas, and also in deeper water in the Atlantic, and 

 in the Florida Channel, where they have been dredged by Pourtales. Beyond a depth 

 of 2,500 fathoms, life is not abundant. 



A living Pleurotoma has been brought up from a depth of 2,090 fathoms; a Fusas, 

 from 1,207 fathoms ; and Crabs ( Gonoplax and Geryon). from 808 fathoms ; all with good 

 eyes; Lobsters (Astacus, etc.), from 1,000 to 1,900 fathoms, without eyes; other Crus- 

 taceans, from over 1,000 fathoms (one near Phronima, three and a half inches long), 

 with perfect eyes. Mollusks are not common at great depths; but there are numerous 

 Starfishes, Echini, and Crinoids; and siliceous Sponges, some of great size and beauty, 

 are very common. The bottom, down to 2,500 fathoms, is, to a great extent, covered 

 — how deeply is unknown — with Foraminifers (shells of Rhizopods), among which 

 the Globigerina is very prominent, giving the name of globigerina mud or ooze to the 

 material ; the beds are similar in nature and origin to those of Chalk. Microscopic 

 calcareous disks, called Coccolitks (p. 135), are also abundant, and, in large accumula- 

 tions, the equally microscopic siliceous Diatoms. Sea-weeds, apart from the micro- 

 scopic Algae, are seldom met with, below 50 fathoms. 



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

 temperature. Some of the simpler Algas, 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° 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 198°, and many Oscillatoi-iw 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 tire several Geyser Basins, in the Yellowstone National 

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



