414 



A JOURNEY m BRAZIL. 



present frequent traces of cross-stratification, alternating 

 with regularly stratified horizontal beds, with here and there 

 an intervening layer of clay. It would seem as if the char- 

 acter of the water-basin had now changed, and as if the 

 waters under which this second formation was deposited 

 had vibrated between storm and calm, had sometimes 

 flowed more gently, and again had been tossed to and fro, 

 giving to some of the beds the aspect of true torrential 

 deposits. Indeed, these sandstone formations present a 

 great variety of aspects. Sometimes they are very regu- 

 larly laminated, or assume even the appearance of the hard- 

 est quartzite. This is usually the case with the uppermost 

 beds. In other localities, and more especially in the lower- 

 most beds, the whole mass is honeycombed, as if drilled by 

 worms or boring shells, the hard parts enclosing softer sands 

 or clays. Occasionally the ferruginous materials prevail to 

 such an extent that some of these beds might be mistaken 

 for bog-ore, while others contain a large amount of clay, 

 more regularly stratified, and alternating with strata of 

 sandstone, thus recalling the most characteristic forms 

 of the Old Red or Triassic formations. This resemblance 

 has, no doubt, led to the identification of the Amazonian 

 deposits with the more ancient formations of Europe. At 

 Monte Al^gre, of which I shall presently speak more in 

 detail, such a clay bed divides the lower from the upper 

 sandstone. The thickness of these sandstones is extremely 

 variable. In the basin of the Amazons proper, they hardly 

 rise anywhere above the level of high water during the rainy 

 season ; while at low water, in the summer months, they may 

 be observed everywhere along the river-banks. It will be 

 seen, however, that the limit between high and low water 

 gives no true measure of the original thickness of the whole 

 series. 



