OPINIONS OF EAELY WOBKEES 153 



promoting the decomposition of igneous rocks, wMle Brongniart, 

 writing with particular reference to feldspathic decomposition 

 and the origin of kaolin, laid great stress on the acceleration 

 of the ordinary process of decay through the electric currents 

 resulting from the contact of heterogeneous rock masses. Dar- 

 win^ believed the extensive decomposition observed by him in 

 Brazil, to have t^ken place under the sea, and before the present 

 valleys were excavated. Hartt^ gave it as his opinion that the 

 decomposition was due to the action of warm rain water soaking 

 through the rock, and carrying with it carbonic acid derived 

 not only from the air, but from the vegetation decaying in the 

 soil as well, together with organic acids, nitrate of ammonium, 

 etc. Further, that the decomposition had gone on only in re- 

 gions once covered by forests. Heusser and Claraz^ suggested 

 that the decomposition was brought about through the influence 

 of nitric acid. ^'It is without doubt determined by the violence 

 and frequency of the tropical rains, and by the dissolving action 

 of water, which increases with the temperature. It is necessary 

 to observe, moreover, that this water contains some nitric acid, 

 on account of the thunder storms which follow each other with 

 great regularity during many months of the year." 



Belt,^ in discussing the extensive decomposition observed by 

 him in Nicaragua, wrote: ''This decomposition of the rocks 

 near the surface prevails in many parts of tropical America, 

 and is principally, if not always, confined to the forest regions. 

 It has been ascribed, and probably with reason, to the percola- 

 tion through the rocks of rain water charged with a little acid 

 from the decomposing vegetation." Hunt^ thought the great 

 amount of decomposition observed by him in the Blue Ridge of 

 Virginia was a matter of great geological antiquity, and effected 

 at a time when a highly carbonate atmosphere and climate quite 

 different from the present prevailed. 



The elder Agassiz laid much stress on the decomposing effects 

 of the hot water from rainfall,® while Mills and Branner,^ in 



^ Geological Observations, p. 417. 



^Pliys. Geog. and Geol. of Brazil. 



'Ann. des Mines, Sth series, Vol. 17, 1860, p. 291. 



* The Naturalist in Nicaragua, 1874. 



«* Proe. Boston Soe. Nat. Hist., Vol. 16, 1873. 



* Journey in Brazil, p. 89. 



^Bull. Geol. Soc. of America, Vol. VII, 1896, also Journal of Geology, 

 Vol. VIII, 1900. 



