292 GEOLOGY OF 



Negro, were lost, and I have therefore very few materials to go 

 upon. 



GrnmV ipems to-bf^ in South America, more extensively 

 developed than in any other part of the world. Darwin and 

 Gardner found it in every part of the interior of Brazil, in La 

 Plata, and Chile. Up the Xingu" Prince Adalbert met with 

 it. Over the whole of Venezuela and New Granada, it was 

 found by Humboldt. It seems to form all the mountains in 

 the interior of Guiana, and it was met with by myself over the 

 whole of the upper part of the Rio Negro, and far up the 

 Uaupes towards the Andes. 



From what I could see of the granitic formation of the 

 Upper Rio Negro, it appeared to be spread out in immense 

 undulating areas, the hollows of which, being filled up with 

 alluvial deposits, form those beds of earth and clay which occur, 

 of various dimensions, everywhere in the midst of the granite 

 formation. In these places grow the lofty virgin forests, while 

 on the scantily covered granite rocks, and where beds of sand 

 occur, are the more open catinga forests, so different in their 

 aspect and peculiar in their vegetation. What strikes one 

 most in this great formation, is its almost perfect flatness. 

 There are no ranges of mountains, or even slightly elevated 

 plateaus ; all is level, except the abrupt peaks that rise suddenly 

 from the plain, to a height of from one hundred to three thou- 

 sand feet. In the Upper Rio Negro these peaks are very 

 numerous. The first is the Serra de Jacami, a little above 

 vSt. Isabel ; it rises immediately from the bank of the river, on 

 the south side, to a height of about six hundred feet. Several 

 others are scattered about, but the Serras de Curicuriarf are 

 the most lofty. They consist of a group of three or four moun- 

 tains, rising abruptly to the height of near three thousand feet ; 

 towards their summits are immense precipices and jagged 

 peaks. Higher up, on the same river, is another group of 

 rather less height. On the Uaupes are numerous hills, some 

 conical, others dome-shaped, but all keeping the same character 

 of abrupt elevations, quite independent of the general profile 

 of the country. About the falls of the river Uaupes there are 

 small hills of granite, broken about in the greatest confusion. 

 Great chasms or bowls occur, and slender pillars of rock rise 

 above the surrounding forest like dead trunks of giant trees. Up 

 the river Isanna, the Tunuhy mountains are a similar isolated 



