Chap. V AND DENUDATION. 237 



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 Yerde 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 y^-q-q of an 

 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, 



