422 A JOURNEY IN BRAZIL. 



founded with the mud deposits of the river. These latter, 

 however, never rise so high as the ochraceous clay, but 

 are everywhere confined within the limits of high and 

 low water. The islands also, in the main course of the 

 Amazons, consist invariably of river-mud ; while those 

 arising from the intersection and cutting off of portions 

 of the land by diverging branches of the main stream 

 always consist of the well-known sandstones, capped by 

 the ochre-colored clay. 



It may truly be said that there does not exist on the 

 surface of the earth a formation known to geologists re- 

 sembling that of the Amazons. Its extent is stupendous ; 

 it stretches from the Atlantic shore, through the whole 

 width of Brazil, into Peru, to the very foot of the Andes. 

 Humboldt speaks of it " in the vast plains of the Amazons, 

 in the eastern boundary of Jaen de Bracamoros," and 

 says, " This prodigious extension of red sandstone in the 

 low grounds stretching along the east of the Andes is 

 one of the most striking phenomena I observed during 

 my examination of rocks in the equinoctial regions." 

 When the great natural philosopher wrote these lines, he 

 had no idea how much these deposits extended beyond 

 the field of his observations. Indeed, they are not limited 

 to the main bed of the Amazons ; they have been fol- 



* Bohn's edition of Humboldt's Personal Narrative, Chap. II. p. 134. Hum- 

 boldt alludes to these formations repeatedly : it is true that he refers them to 

 the ancient conglomerates of the Devonian age, but his description agrees so 

 perfectly with what I have observed along the banks of the Amazons and 

 the Rio Negro that there can be no doubt he speaks of the same thing. He 

 wrote at a time when many of the results of modern geology were un- 

 known, and his explanation of the phenomena was then perfectly natural. 

 The passage from which the few lines in the text are taken shows that these 

 deposits extend even to the Llanos. 



