THE ATMOSPHERE AS A MECHANICAL AGENT. 163 



Bahamas, Key West and elsewhere on the Florida Banks, and also on 

 Oahu and other Hawaiian Islands. 



2. Eolian transportation of volcanic ashes. — The transportation of volcanic 

 ashes usually takes place without drifting, and the bedding, therefore, is 

 commonly horizontal. In 1812, ashes were carried from a volcano on St. 

 Vincent to Barbados, 60 to 70 miles; and in 1835, from the volcano of 

 Coseguina in Guatemala to Jamaica, a distance of 800 miles. In 1883, the 

 dust from the volcano of Krakatoa, an island just west of Java, was thrown 

 to a height of 50,000 feet, according to Verbeck, and continued to be pro- 

 jected for 36 hours ; and it is supposed that the ashes made the circuit of 

 the globe, and were the cause of the sunset glows of the following autumn. 

 The bottom of the Pacific has been found to be very generally covered with 

 volcanic ashes derived from its many volcanoes. 



3. Eolian transportation of living species or their relics. — A tornado that 

 becomes what is known as a " water-spout " over a large river or lake, carry- 

 ing up at its center great quantities of water, will take up the ova and 

 smaller life of the waters, and transfer them to other places, and may thus 

 contribute new species to distant lakes or rivers. Land Birds and Insects 

 are sometimes drifted far out to sea, and so reach oceanic islands, and some- 

 times in the case of Birds another continent. Seeds of many kinds go with 

 the winds. A Spider of the ballooning kind, Sarotes venatoriiis, has probably 

 traveled around the globe, according to H. C. McCook, crossing oceans and 

 continents, and thus has gained a world-wide distribution. A related species 

 is reported by Darwin as suddenly appearing on the rigging of the "Beagle " 

 60 miles from the land. 



Showers of grayish and reddish dust sometimes fall on vessels in the 

 Atlantic off the African coast, and over southern Europe (producing, when 

 they come down with rains, "blood-rains"), the particles of which, as first 

 shown by Ehrenberg, are largely microscopic organisms. The figures on 

 the following page represent the species from a single shower, near Lyons, 

 on October 17, 1846. The whole amount which fell was estimated by 

 Ehrenberg at 720,000 pounds ; and of this, one eighth, or 90,000 pounds, 

 consisted of these organisms. 



The species figured by Ehrenberg (Passat- Staub und Blut-Regen, 4to, 1847, and 

 Amer. Jour. Sci., II. xi. 372), include 39 species of siliceous Diatoms (Fig. 157, 1-65); 25 

 of what he calls Phytolitharia (Fig. 157, 66-104), besides 8 Rbizopods. The following are 

 the names of the Diatoms : _ 



Nos. 1, 2, Melosira granulata; 3, M. deciissata; 4, M. Marchica; 5-7, M. distans ; 

 S.9, Coscinodiscus atmosphericus ; 10, Coscinodiscus (?) ; 11, Trachelomonas levis ; 12, 

 Campylodiscus clypeus ; 13-16, Gomphonema gracile ; 16, 17, Cocconema cymhiforme ; 

 18, Cymhella mamdata ; 19, 20, Epithemia longicornis ; 21, 22, E. longicornis ; 23, E. 

 Argus; 24, E. longicornis; 25, Eunotia granulata (?) ; 26, E.'zebrina (?) ; 27, Him- 

 antidium Monodon (?) ; 28-32, Eunotia amphioxys; 33, 34, Epithemia gibbenila; 35, 

 Eunotia zebrina (?) ; 36, E. zygodon (?) ; 37, Epithemia gibba; 38, Eunotia tridentula; 

 39, E. (?) Icevis ; 40, Himantidium arcus ; 41, 42, Tabellaria ; 43, Odontidiimi (?) ; 

 44, Cocconns lineata ; 45, C. ntmn spheric a ; 46, Navicula bacillum ; 47, jSF. amphioxys ; 



