ATLAS ATMOSPHERE 81 on his head and hands. Some stories repre- sent him as a great astronomer, king, and demi- god, who first taught man that heav?n had the form of a globe. Ovid relates that Perseus, having been refused shelter by Atlas, changed him by means of the head of Medusa into Mount Atlas, on which rested the firmament. ATLAS (Moorish, Adrar, Dir, Jebel Tidla, or Jebel Adla), a mountain system of N. W. Africa, forming the watershed between the Mediterranean sea and the Sahara. It ex- tends under various names from Cape Ghir on the Atlantic to the gulf of Cabes (or Lesser Syrtis), about 1,200 m. It is generally divi- ded into the Greater and Lesser Atlas, and a middle table land. The Lesser Atlas is the range nearest the seacoast ; the Greater bor- ders on the desert. But this division, originated by Ptolemy, is unknown to the natives, and no real line of division can be ascertained. In Morocco the Atlas is a continuous chain from which the country slopes N. W. and S. E. toward -the sea and the desert ; and here it attains its greatest altitude, some of the peaks, as Jebel Miltzin, approaching, and others ex- ceeding 12,000 ft. in height. The height of the mountains generally diminishes toward the east. The middle part in Algeria is divided into the range of the Tell, between the Medi- terranean and the Shott plateau or salt swamps, and the range of the Sahara, between the pla- teau and the desert. The Tell consists of single groups of mountains separated from each other by wide valleys, of which 11 are counted from W. to E. In Algeria the highest point is Jebel Sheliha, S. of Constantino, upward of 7,000 ft. ; and Jurjura or Jerjera, between Algiers and Constantine, is upward of 6,000. The chain mainly follows a direction parallel to the coast, but then turns S. E., and takes the name of Jebel Aures, and approaching the coast again, it penetrates into the territory of Tunis. There are several passes, of which the chief is in the Jurjura, the famous Biban, a long, narrow val- ley bordered by rocks rising precipitously 150 to 200 yards. In the western part of the range is the Bebaoum pass, leading to Tarudant in Morocco, also bounded by perpendicular rocks and precipices. Another defile, frequented by caravans, leads from Fez to Tafilet. East of the city of Morocco snow covers the summits nil the year; in Algeria it falls in September and melts in May. The climate is generally very salubrious. The sides of the mountains are covered with forests of oak, cedar, pine, pistachio, cypress, olive, and oleander. The Kabyles occupy the habitable parts of the At- las. The wild animals are the lion, panther, guepard, hyama, boar, and bear; and several -p'Ties of monkey are also found. None of the rivers are navigable, and many are only winter torrents. The Tensift and Draa flow into the Atlantic; the Tafilet is lost in the sands; the Shelliif, the Seybuse, the Kebir, the Rumel, and the Mejerda flow into the Mediterranean. According to a description of a branch of the I Greater Atlas from S. to N. near Jebel Miltzin given by the English naturalist Washington, the geological constitution of this part of the range is gneiss, schist, red sandstone, transition limestone, and marl. Capt. Rozet gives the j following description of the Lesser Atlas after I a careful study : The country of Algeria, cover- ed by branches or plateaus of the Lesser Atlas, ' is composed of transition schist, gneiss, blue limestone similar to English lias, deposits of alluvium, trachytic porphyry, diluvium, and ! other deposits. The prevailing rock is a whi- tish green or blue schist in deformed layers, broken up into numerous fissures filled with white quartz and oxidized iron. The limestone enclosed in the schist is of a saccharoid texture, and of a gray or dark blue color ; it forms con- siderable masses in the mountains of Algeria. The schistose stratum contains garnet and anthracite ; it gradually changes to mica schist and then to gneiss. The alluvium is composed of horizontal strata of clay, marl, and rounded pebbles. The mineral wealth of the Atlantic Atlas is but imperfectly known. The Greater Atlas seems to be crossed by veins of copper, iron, tin, antimony, and perhaps gold and sil- ver. The Lesser Atlas has mines of lead and iron; silver, copper, mercury, and plumbago are also found. There are many mineral springs in different parts. ATMOSPHERE (Gr. ar/i6f, vapor, and o<j>aipa, sphere), or Air, the gaseous envelope of a celes- tial body or of the earth. At present we know that the sun and planets possess atmospheres, and the revelations of the spectrum begin to show what these atmospheres consist of. That of the sun contains, besides hydrogen and other gases, the vapors of solids and liquids, so highly heated that iron vapor is one of its principal constituents. The atmospheres of Venus and Mars appear similar to that of the earth ; those of Jupiter and Saturn, Uranus and Neptune, dif- fer so much from our terrestrial atmosphere, that it is highly probable that these planets possess so high a temperature as not only to keep many solids in the state of vapor, but even to be slightly self-luminous. The moon shows no trace of an atmosphere. When we consider the great amount of oxygen and water combined with the solid portions of our earth's surface, it is highly probable that the volcanic scoria? and lavas of the moon have long ago absorbed all the air and water which may once have enveloped it. The at- mosphere has been the principal agent in transforming the surface of our earth into what it is: first by disintegrating the rocks; then, in connection with solar heat, starting vegetation ; then causing the decay of organic substances, and so forming soil for more pro- fuse organic growth, giving sustenance for the animal kingdom; and finally fulfilling all the functions necessary for the development of all forms of life. The functions of the atmosphere are : to act as the principal conductor of sound waves; to moderate the solar heat, admitting
