WATER. 635 



twenty-five of what he calls Phytolitharia (Figs. 66-104), besides eight of Rhizopods. 

 The following are the names of the Diatoms. 



Figs. 1, 2, Melozira granulata ; 3, M. decussata ; 4, M. Marchica ; 5-7, M. distans ; 

 8, 9, Coscinodiscus atmospherica ; 10, Coscinodiscus (?) ; 11, Trachelomonas levis ; 12, 

 Camjyylodiscus clypeus ; 13-15, Gomphonema gracile ; 1G, 17, Cocconema cymbiforme ; 

 18 Cymbella maculata; 19, 20, Epithemia hngicornis ; (frustule of E. Argus); 21, 22, 

 E. hngicornis; 23, E. Argus; 24, E. longicornis; 25, Eunotia granulata (?) ; 26, E. 

 zebrina (?) ; 27, Himantidium Monodon (?) ; 28-32, Eunotia amphioxys ; 33, 34, Epithemia 

 gibberula ; 35, Eunotia zebrina (?) ; 36, E. zygodon (?) ; 37, Epithemia gibba ; 38, Eu- 

 notia tridentula ; 39, E. (?) levis; 40, Himantidium arcus ; 41, 42, Tabellaria ; 43, 

 Odontidium(?) ; 44, Cocconeis lineata ; 45, C atmospheHca ; 46, Navicula bacillum ; 47, 

 A', amphiuxys; 48, 49, A. semen; 50, A", serians ; 51, Pinnularia borealis ; 52, P. 

 riridula ; 53, P.viridis; 54, Mastogloia (?) ; 55, Pinnularia mqualis (?) ; 56, Surirella 

 craticula (?) ; 57, 58, Synedra ulna ; 59, Odontidium (?) ; 60, Fragilaria pinnata (?) ; 61, 

 Mastogloia (?) ; 62-65, doubtful. 



A shower which happened near the Cape Verdes, and has been described by Darwin, 

 had by his estimate a breadth of more than 1,600 miles, — or, according to Tuckey, of 

 1,800 miles, — and reached 800 or 1,000 miles from the coast of Africa. These numbers 

 give an area of more than a million of square miles. 



In 1755, there was a " blood-rain " near Lago Maggiore, in northern Italy, covering 

 about two hundred square leagues, which made an earth-deposit in some places an inch 

 deep; if averaging two lines in depth, the amount for each square mile would equal 

 2,700 cubic feet. The red color of the " blood-rain " is owing to the presence of some 

 red oxyd of iron. 



Ehrenberg enumerates a large number of these showers, citing one of the earliest from 

 Homer's Iliad, and among those whose deposits he examined he distinguished over 

 three hundred species of organisms. The species, so far as ascertained, are not African, 

 and fifteen are South American; but the origin of the dust is yet unknown. The zone 

 in which these showers occur covers southern Europe and northern Africa, with the ad- 

 joining portion of the Atlantic, and the corresponding latitudes in western and middle 

 Asia. 



IV. WATER. 



Water takes the lead among geological agencies, both as regards 

 mechanical and chemical work. It has been, through the ages, the 

 chief instrument in rock-making, in shaping mountains, and excavating 

 valleys, and in recording the progress of the earth in its features and 

 life. It has worked in each of its three states, vapor, water, and ice, 

 and in the passage from one state to another ; in all these conditions 

 doing mechanical work, and in those of water and vapor, especially, 

 chemical work. In some of its operations it has had the aid of heat, 

 and these are treated beyond under that head. 



An important part of its mechanical work is that of weakening co- 

 hesion, or softening rocks, as well as earthy beds, by penetrating them 

 or becoming absorbed by them, as briefly brought out on page 629. 

 By this quiet process, and the no less quiet chemical methods explained 

 beyond, it has aided much in preparing the way for its three great 

 labors — erosion, transportation, and deposition. 



Water, unlike the air, whose currents are the wayward winds, has 

 an upper surface, and this gives it a cutting edge for erosion, and a 



