ATMOSPHERE. 631 



ma cymbiforme; 18, Cymbella maculata ; 19, 20, Epithemia longicornis (frustule 

 of E. Argus); 21, 22, E. longicornis; 23, E. Argus; 24, E. longicornis; 25, Eu- 

 notia granulata? ; 26, E. zebrina? ; 27, Himantidium Monodon? ; 28-32, Euno- 

 tia amphioxys ; 33, 34, Epithemia gibberula ; 35, Eunotia zebrina f ; 36, E. zygo- 

 don? ; 37, Epithemia gibba ; 38, Eunotia tridentula ; 39, E.t levis ; 40, Himan- 

 tidium Arcus; 41,42, Tabellaria ; 43, Odontidium? ; 44, Coccone'is lineata ; 45, 

 (7. atmospherica ; 46, Navicula Bacillum ; 47, iV. amphioxys ; 48, 49, A 7 ". Semen; 

 50, i\T. serians ; 51, Pinnularia borealis ; 52, P. viridula ; 53, P. viridis ; 54, 

 Mastogloia ? ; 55, Pinnularia aqnalis ? ; 56, Surirella Craticula t ; 57, 58, Synedra 

 Ulna ; 59, Odontidium ? ; 60, Fragilaria pinnata f ; 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 

 1600 miles, — or, according to Tuckey, of 1800 miles, — and reached 800 

 or 1000 miles from the coast of Africa. These numbers give an area 

 of more than a million of square miles. 



Dust from a shower over Italy in 1803 afforded Ehrenberg forty- 

 nine species of organisms, and another in 1813 over Calabria, sixty- 

 four species ; and the two had twenty-eight species in common. 



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

 Italy, covering about 200 square leagues ; and at the same time 

 nine feet of reddish snow fell on the Alps. The earthy deposit in 

 some places was an inch deep. Supposing it to average but two 

 lines in depth, it would be for each square English mile an amount 

 equal to 2700 cubic feet. The red color of the " blood-rain" is owing 

 to the presence of some red oxyd of iron. 



Ehrenberg enumerates a very large number of these showers, re- 

 ferring to Homer's Iliad for one of the earliest known, and asks, 

 With such facts before us, how many thousand millions of hundred- 

 weight of microscopic organisms have reached the earth since the 

 period of Homer? The whole number of species made out is 

 over 300. 



The species, as far as ascertained, are not African ; 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 adjoining portion of the Atlantic, and 

 the corresponding latitudes in western and middle Asia. 



5. Sand-scratches. — The sands carried by the winds, when passing 

 over rocks, sometimes wear them smooth, or cover the surface 

 with scratches and furrows, as observed by Wm. P. Blake over 

 granite rocks at the Pass of San Bernardino in California. Even 

 quartz was polished, and garnets were left projecting upon pedicels 

 of feldspar. Limestone was so much worn as to look as if the sur- 

 face had been removed by solution. Glass in windows on Cape Cod 

 sometimes has holes worn through by the same means. ( J. Wyman.) 



