Chap. V. AND DENUDATION. 235 



space of 1600 miles in latitude, and for a 

 distance of from 300 to 600 miles from the 

 coast. But dust has been seen to fall at a 

 distance of 1030 miles from the shores of 

 Africa, During a stay of three weeks at 

 St. Jago in the Cape Verde Archipelago, the 

 atmosphere was almost always hazy, and ex- 

 tremely fine dust coming from Africa was con- 

 tinually falling. In some of this dust which 

 fell in the open ocean at a distance of between 

 330 and 380 miles from the African coast, there 

 were many particles of stone, about xttott ^^ ^" 

 inch square. Nearer to the coast the water 

 has been seen to be so much discoloured by 

 the falling dust, that a sailing vessel left a 

 track behind her. In countries, like the Cape 

 Yerde Archipelago, where it seldom rains 

 and there are no frosts, the solid rock never- 

 theless disintegrates ; and in conformity with 

 the views lately advanced by a distinguished 

 Belgian geologist, De Koninck, such disin- 

 tegration may be attributed in chief part to 

 the action of the carbonic and nitric acids, 

 together with the nitrates and nitrites of 

 ammonia, dissolved in the dew. _ 



In all humid, even moderately humid, 



