GEOLOGY OF THE AMAZONIAN VALLEY. 319 



on the higher ground, open dry plains with scanty vegeta- 

 tion, — the ground in the water-courses or gullies, formed of 

 clay, being baked by the heat of the sun into slate-like 

 masses. One of these spots we now reach. The most pro- 

 minent plants of this sandy or clayey region are clusters of 

 cacti and curua palms — a kind of stemless, low palm, with 

 broad leaves springing, vase-like, from the ground. Here 

 also grow wild pine-apples; and in broad sunlight numerous 

 humming-birds delight to sport and feed upon the blossoms 

 of the various plants which find no room to bloom in the 

 darker shades of the forest. 



GEOLOGY OF THE AMAZONIAN VALLEY. 

 Professor Agassiz remarks that no formation— -known to 

 geologists — resembling that of the Amazon exists on the face 

 of the earth. 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 — one vast extent of red 

 sandstone, capped by a yellow-ochred clay ; not only along the 

 banks of the main river, but forming the sides of those of its 

 tributaries, to their far-off sources, probably over the whole 

 basin of the Paraguay and the Rio de la Plata, How are 

 these vast deposits formed ? is the question. The easiest 

 answer, he observes, and the one which most readily sug- 

 gests itself, is that of a submersion of the continent at suc- 

 cessive periods — to allow the accumulation of these materials 

 — and its subsequent elevation. This explanation is rejected, 

 for the simple reason that the deposits show no signs what- 

 ever of a marine origin. No sea-shells, or remains of any 

 marine animal, have as yet been found throughout their whole 

 extent — over a region several thousands of miles in length, 



