NOTES ON GEOLOGY. 425 



The then newly opened prolongation of the Estrada de Ferro Dom 

 Pedro II. to Queluz de Minas was thus affected in January, 1884, 

 and a long bank had to be remade, causing a stoppage of traffic 

 for some weeks. M. Liais considers the decomposition of the 

 gneiss to be wholly due to atmospheric causes. Mr. Darwin 

 thinks that it took place at a period of subsidence under the sea 

 before the valleys were carved out.* Mr. C. F. Hartt, who 

 accompanied M. Agassiz in his explorations in Rio, Bahia, and 

 the Amazon valley, believes "that it has taken place only in 

 regions anciently or at present covered by forest," and says, " This 

 decomposition results, in my opinion, from the action of the warm 

 rain-water soaking through the rock and carrying with it carbonic 

 acid, derived not only from the air, but from the vegetation 

 decaying upon the soil, together with organic acids, nitrate of 

 ammonia," etc. He states that the same phenomena is observed 

 near New York and in the Neilgherries. M. Agassiz in his 

 " Journal in Brazil," j lays great stress on glacial action. This is 

 a matter which deserves a few remarks, as it is of paramount im- 

 portance. 



I never observed any transported blocks, or striations, or roches 

 moutonnees, or anything that could be considered as glacial drift. 

 M. Agassiz is obliged to admit that he never saw any striations 

 which are such a characteristic feature of glacial phenomena, but 

 attributes their disappearance to atmospheric decomposition. 

 Mr. Hartt began his explorations strongly opposed to the glacial 

 theory ; but the result of his examinations and intercourse with 

 M. Agassiz led him fully to acquiesce in the professor's theory of 

 glaciation. I must be content with summarizing in a few words 

 M. Liais's statement, and confess that I lean strongly to accepting 

 his views. I may also state that Dr. G. S. de Capanema, in his 

 work, " Decomposicao dos Penedos do Brazil," J disbelieves in 

 the glacial origin of the surface deposits claimed by Professor 

 Agassiz and Mr. Hartt to be drift, and rather considers them to 

 be the work of decomposition alone. Mr. Hartt lays much stress 

 on the absence of stratification near the surface, attributing this 



* " Geological Observations," p. 428. 



t "Geological and Physical Geography of Brazil," p. 25. 



j Published at Rio, 1866. 



