426 A JOURNEY IN BRAZIL. 



or reducing thorn to small pebbles, and it must have 

 accumulated at its lower end a moraine of proportions 

 as gigantic as its own ; thus building a colossal sea-wall 

 across the mouth of the valley. I shall be asked at once 

 whether I have found here also the glacial inscriptions, 

 the furrows, stria3, and polished surfaces so character 

 istic of the ground over which glaciers have travelled. 

 I answer, not a trace of them ; for the simple reason that 

 there is not a natural rock-surface to be found through 

 out the whole Amazonian Valley. The rocks themselves 

 are of so friable a nature, and the decomposition caused 

 by the warm torrential rains and by exposure to the 

 burning sun of the tropics so great and unceasing, that 

 it is hopeless to look for marks which in colder climates 

 and on harder substances are preserved through ages un 

 changed. With the exception of the rounded surfaces 

 so well known in Switzerland as the roches moutonnees 

 heretofore alluded to, which may be seen in many locali 

 ties, and the boulders of Erere*, the direct traces of gla 

 ciers as seen in other countries are wanting In Brazil. 

 I am, indeed, quite willing to admiriiliat, from the nature 

 of the circumstances, I have not here the positive evidence 

 which has guided me in my previous glacial investigations. 

 My conviction in this instance is founded, first, on the 

 materials in the Amazonian Yalley, winch &quot;correspond 

 exactly in their character to materials accumulated in 

 glacier bottoms ; secondly, on the resemblance, of the upper 

 or~4hicd ^Amazonian formation to the Rio drift,* of the 



* As I have stated in the beginning, I am satisfied that the unstratified 

 clay deposit of Rio and its vicinity is genuine glacial drift, resulting from the 

 grinding of the loose materials interposed between the glacier and the solid 

 rock in place, and retaining to this day the position in which it was left by the 

 ice. Like all such accumulations, it is totally free from stratification. If this 



