4 VIEW OF THE FAUNA OF BRAZIL 



quently of considerable extent. This siliceous stratum has 

 no uniform depth in the clay, but often approaches the sur- 

 face, and then forms the ' Gruns Campos' so characteristic of 

 that country, and so unfriendly to agriculture, though clothed 

 with so peculiar a vegetation. Amongst this quartz occur, 

 although sparingly, fragments of other rocks, particularly of 

 ironstone. ' The colour of the clay occasionally passes from 

 red into dull ochre-yellow : and this change in colour is usu- 

 ally accompanied by a greater degree of fineness and unifor- 

 mity of composition, with some slight trace of cleavage, or 

 separation into cubical masses. I have hitherto had no op- 

 portunity of observing these beds of clay alternating with beds 

 of sand ; whereas this last formation appears on the surface 

 over an extent of many degrees in length, in the broad vale 

 watered by the St. Francisco river. 



But the most peculiar character under which these newest 

 formations present themselves in Brazil, is that called in this 

 country " Tapanhoacanga," or negro-head. This formation 

 is seen, like a stream of lava, spread over the plains, valleys, 

 and hills, nay, even on the highest mountain-ridges of Brazil. 

 It is most common in those districts where there are iron- 

 stone rocks of the older formations. It consists of a ferrugi- 

 nous conglomerate, composed of rolled and angular fragments 

 of quartz, and other rocks of the country ; but chiefly of the 

 iron formation itself, such as ferriferous mica slate &c., united 

 by a ferruginous cement of red, yellow, or black colour. Oc- 

 casionally, the fragments disappear, and the cementing sub- 

 stance alone remains. It forms a mass almost as hard as 

 stone, with a smooth and often shining surface ; inside, it is 

 full of vescicular holes, which give it the appearance of a slag. 

 It very often contains stone marrow, and in general the same 

 minerals that form the constituent portions of the common red 



* The origin of this quartz-ted was long a puzzle to me, until more care- 

 ful examinations of the principal mountain range enlightened me on the 

 subject. One of the most important members in the composition of that 

 range is a vast mass of talc slate, with numerous veins and subordinate beds 

 of quartz. This talc slate, in most places, and to considerable depths, is 

 in such a state of decomposition, as to crumble between the fingers, and 

 the quartz separates with the touch into larger or smaller angular frag- 

 ments. If we examine the beds of diluvium at the foot of this mountain 

 chain, we there see the red homogeneous clay replaced by a mass of nothing 

 but fragments of talc slate, lying in all directions, but containing also the 

 same siliceous layers disposed with more regularity, so as often to look like 

 connected quartz beds. That this talc slate is in a secondary position, is 

 evident from its irregular stratification ; and if we follow its development 

 from the foot of the mountain, it is easy to convince ourselves of its gradual 

 passage and change into the common red clay, with its usual siliceous bed. 



