ATLANTIS 



463 



ATOLL 



regions to 28 F. on the borders of the Arctic 

 Ocean. In the tropical regions the temperature 

 falls rapidly for the first 1,500 feet of descent, 

 but below that depth the change is less rapid. 

 The water on the bottom of the ocean is near 

 the freezing point, and changes but little. 



Currents. The North and South Atlantic 

 each has a system of marine currents, or rivers 

 in the ocean. In the North Atlantic the most 

 noted of these is the Gulf Stream (which see), 

 which carries the warm water from the tropical 

 regions northward and then eastward, making 

 the western coast of Europe much warmer than 

 the eastern coast of North America in the same 

 latitude. Flowing southward between the Gulf 

 Stream and the coast is the Labrador Current, 

 a cold water stream which brings many ice- 

 bergs into the warmer regions where they melt 

 and disappear, but in the meantime they are a 

 great menace to navigation (see ICEBERG). The 

 system in the South Atlantic is similar to that 

 in the North Atlantic (see OCEAN CURRENTS). 



Life. The Atlantic Ocean is one of the great- 

 est sources of food supply in the world. Most 

 of the fish supplied to the nations of Europe 

 and America are taken from the Atlantic, and 

 the most important of these are the herring 

 and the cod. The most extensive fishing 

 grounds are on and near the Grand Banks, off 

 Newfoundland, and the Dodder Banks, in the 

 North Sea. To the fish taken in such large 

 quantities from these sources must be added 

 the tons of oysters and other shell fish and 

 the fish caught in the innumerable branches of 

 the ocean. Sponges are obtained off the coast 

 of Florida and in the Mediterranean, and the 

 tropical seas are filled with millions of minute 

 creatures, which, while they do not add any- 

 tin ng to supply man's needs, beautify the sea 

 by the phosphorescent linht which they emit. 

 In the greatest depths giant fish hitherto un- 

 known are being discovered. See OCEAN; 

 TIDES; WAVES. W.FJ. 



ATLAN'TIS, an island which, according to 

 ancient tradition, existed in the Atlantic Ocean 

 near the Pillars of Hercules (Strait of Gibral- 

 tar). Plato wrote of it, declaring tint it had 

 been the home of a great nation but had finally 

 been swallowed up by the sea. Some investi- 

 gators believe that at the earliest dawn of 

 tradition tli. re may have been such an island, 

 but others regard the whole legend as tin- 

 outgrowth of some pre-historic discovery of 

 NYw World. 



AT'LAS, in th< mythology of the M 



:tan whom Zeus condemned to 



THE MYTH- 

 ICAL ATLAS 



bear the heavens on his shoulders. Through 

 the centuries he stood, almost fainting with 

 weariness, until Perseus came by, bearing the 

 head of the Gorgon, Medusa, 

 which turned all who looked 

 upon it into stone. At Atlas' 

 request, Perseus held up the 

 head, and the giant was 

 changed into the mountains 

 which bear his name. When 

 the earliest collection of maps 

 appeared it bore on its title- 

 page the picture of Atlas 

 bending under the weight of 

 the earth, and such books 

 have therefore been called 

 atlases to this day. 



ATLAS MOUNTAINS, the name given to 

 the chains of mountains running parallel to the 

 north coast of Africa from Cape Nun on the 

 Atlantic Ocean, across Morocco, Algiers and 

 Tunis to the Gulf of Gabes on the Mediter- 

 ranean, a distance of 1,500 miles. These ranges 

 are named after Atlas, who, according to an- 

 cient mythology, supported on his shoulder the 

 vault of the heavens and dwelt in the moun- 

 tains. The interesting story is told in the 

 article ATLAS. The mountains are roughly 

 divided into two main parallel chains, running 

 west to east. The inner or Greater Atlas, lying 

 toward the Sahara, is separated by high 

 plateaus from the lower mountains of the 

 Lesser or Maritime Atlas, along the Mediter- 

 ranean coast. Morocco contains the highest 

 peaks of the system, Jebel Ayashi being 14,600 

 and Tamjurt 14,500 feet above sea level. The 

 mountains contain many minerals, including 

 silver, antimony, lead, copper and iron. Beau- 

 tiful marble is found in many parts of the 

 ranges. The vegetation of the northern and 

 higher regions resembles that of Europe, but 

 the southern slopes, exposed to the hot, dry 

 winds of the Sahara, are generally bare and 

 sandy. 



ATMOSPHERE, at' mos/ecr. See AIR. 



ATMOSPHERIC DUST. See DUST, ATMOS- 

 PHERIC. 



ATOLL, atoll' or at' ol, a picturesque coral 

 island common in the Pacific Ocean, consist inn 

 of a circular strip or ring of coral inclosing a 

 shallow pool or lagoon. The reef usually has 

 a thin covering of soil in which grow palm 

 and breadfruit trees. In many cases the edges 

 of a submerged volcanic crater supply the base 

 <>f the structure The circle of the atoll il 

 usually broken on the side of the. prevail inn 



