The Elements of economic geology

Bibliographic data

Monograph

Identifikator:: 1773832379

URN:: urn:nbn:de:zbw-retromon-172798

Document type:: Monograph

Author:: Gregory, John W. http://d-nb.info/gnd/11683014X

Title:: The Elements of economic geology

Place of publication:: London

Publisher:: Methuen

Year of publication:: 1928

Scope:: XIV, 312 S.; graph. Darst.

Digitisation:: 2021

Collection:: Economics Books

Usage license:: Get license information via the feedback formular.

Chapter

Document type:: Monograph

Structure type:: Chapter

Title:: Part III. Earthy minerals

Collection:: Economics Books

202 ECONOMIC GEOLOGY larger, until this chain of death concentrates phosphorus in the bodies of fish, which are in turn the prey of gluttonous sea birds. Small islands off the coast of South America are the nesting places of vast flocks of a cormorant, Phalacro- corax bougainvillei, which weighs 6 Ib., but will eat 33 lb. of fish at a meal, and from 8 to 10 lb. in a day. They cannot assimilate all the phosphate and it is deposited in their droppings as guano—the Spanish word for dung. The fertilizing value of guano depends also on its nitro- genous constituents, mostly ammonia, which may be washed out by rain, leaving the residue as phosphoric or leached guano. Thick guano deposits can only accumulate on islands where birds can nest safe from mammals and snakes, and in climates with an insignificant rainfall. These con- ditions occur off the western coasts of South America, in “Guano Islands” off South-western Africa, and in the Abrolhos Islands off West Australia, where the prevalent westerly winds pile water against the coast and cause a cold northward flowing current. The Humboldt current along South America is 20° cooler than the adjacent water, and the Antarctic fauna—fur seals, petrels, and penguins—ranges northward into the tropics. The wind that blows across this cold water has its temperature raised on reaching land and its capacity for carrying moisture thereby increased ; hence the sea wind has a parching effect until the air is chilled by rising up the mountains, where its moisture falls as rain. The supplies of guano are to some extent renewed, but the birds have at times suddenly abandoned the islands, as in 1911 when millions of the young were left to die. Dr, H. O. Forbes explained their disappearance as due to fright at an earthquake shock. They began to return three months later, and Forbes estimated that 5,600,000 of them were nesting on the Central Chincha Island in 1913; and that they ate 1000 tons of fish a day.! Rock PuospHATE—In a rainy climate the phosphoric acid is leached out of the bird droppings, and carried into the underlying material which it converts into phosphate. Manv of the bird-frequented islands are coral reefs and L Cf. R. C. Murphy, Bird Islands of Peru, 1925 H. O. Forbes, {bis., 1913 (10), i, pp. 709-12.

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