ALG^. 183 



remarkable resemblance in the colour and character 

 of the dust to that of the Atlantic, Genoa, and Lyons, 

 and an identity in many of the species. Forty-six 

 species out of the sixty-six occur in the Sirocco and 

 Atlantic dust. Twelve species of Diatomacese are 

 common to the Atlantic showers and the Tyrolese 

 snows. This uniformity of character over regions so 

 widely separate, yet in nearly a common latitude or 

 zone, and in so many distinct examples through a 

 number of years, is most surprising. 



Dust also fell in Italy in 1803, and Calabria in 18 13. 

 The former of these showers is represented as coming 

 from the south-east. It afforded forty-nine species, 

 and that of Calabria sixty-four. Out of the forty-nine 

 species thirty-nine have been observed in the more 

 recent showers, and fifty-one of the sixty-four. These 

 showers, ten years apart, have twenty-eight species in 

 common. In both, nearly all the species are of fresh- 

 water or continental origin. 



Ehrenberg remarks that these showers appear to 

 prevail most within a zone extending from the part 

 of the Atlantic off the west coast of Middle and 

 North Africa, along in the direction of the Mediter- 

 ranean Sea, reaching a short distance north of this 

 sea, and continued into Asia between the Caspian 

 Sea and the Persian Gulf, perhaps to Turkestan, 

 Kaschgar, and China ; and they seldom reach north 

 to Sweden and Russia. This zone, according to the 

 observations of Tuckey, has a breadth of eighteen 

 hundred miles in the North Torrid zone. The 

 reddish colour of the dust, as well as the organic 

 forms, show that the dust is not of African origin. 



