12 BAHI A BRAZIL. [chap. i. 



shady parts of the wood. The noise from the insects is so loud, 

 that it may be heard even in a vessel anchored several hundred 

 yards from the shore ; yet within the recesses of the forest a 

 universal silence appears to reign. To a person fond of natural 

 history, such a day as this brings with it a deeper pleasure than 

 he can ever hope to experience again. After wandering about 

 for some hours, 1 returned to the landing-place ; but, before 

 reaching it, I was overtaken by a tropical storm. I tried to 

 find shelter under a tree, which was so thick that it would never 

 have been penetrated by common English rain ; but here, in a 

 couple of minutes, a little torrent flowed down the trunk. It is 

 to this violence of the rain that we must attribute the verdure 

 at the bottom of the thickest woods : if the showers were like 

 those of a colder clime, the greater part would be absorbed or 

 evaporated before it reached the ground. I will not at present 

 attempt to describe the gaudy scenery of this noble bay, because, 

 in our homeward voyage, we called here a second time, and I 

 shall then have occasion to remark on it. 



Along the whole coast of Brazil, for a length of at least 2000 

 miles, and certainly for a considerable space inland, wherever 

 solid rock occurs, it belongs to a granitic formation. The cir- 

 cumstance of this enormous area being constituted of materials 

 which most geologists believe to have been crystallized w r hen 

 heated under pressure, gives rise to many curious reflections. 

 Was this effect produced beneath the depths of a profound ocean ? 

 or did a covering of strata formerly extend over it, which has 

 since been removed ? Can we believe that any power, acting 

 for a time short of infinity, could have denuded the granite over 

 so many thousand square leagues ? 



On a point not far from the city, where a rivulet entered the 

 sea, I observed a fact connected with a subject discussed by 

 Humboldt.* At the cataracts of the great rivers Orinoco, Nile, 

 and Congo, the syenitic rocks are coated by a black substance, 

 appearing as if they had been polished with plumbago. The 

 layer is of extreme thinness ; and on analysis by Berzelius it was 

 found to consist of the oxides of manganese and iron. In the 

 Orinoco it occurs on the rocks periodically washed by the floods, 

 and in those parts alone where the stream is rapid ; or, as the 



* Pers. Narr., vol. v. pt. i. p. 18. 



