SERRA DO ESPINHAQO, BRAZIL 399 



exception and that of the lower beds of the Paraguassii region, the 

 sandstones of the range are to be considered as constituting a geo- 

 logical unit, or not, must also remain in doubt, though I am per- 

 sonally inclined to an afhrmative opinion. 



The geological age of the characteristic rocks of the Serra do 

 Espinhafo zone, and of the orogenetic movement that has given 

 them their present attitude, must also remain in doubt. The most 

 that can be said is that neither is as ancient as has hitherto been 

 supposed, and apparently the Devonian can be taken as the extreme 

 limit of age. This, however, includes the hypothesis, not in itself 

 improbable, of a localization of the orogenetic movement, since the 

 definitely known Devonian deposits of other parts of Brazil (in the 

 states of Parana, Matto Grosso, and Para) were not affected by it. 

 The other extreme age limit is the Cretaceous, but until the Jacobina 

 section is examined, and the reputed find of fossils verified or dis- 

 proved, this hypothesis can neither be accepted nor completely put 

 aside. The hypothesis of a Mesozoic age (Cretaceous or pre-Cre- 

 taceous) is a seductive one, as this would bring into line, at least as 

 regards age, the occurrences of the diamond in various parts of Brazil 

 and in South Africa (17); but against this we have the assumed, 

 though not definitely proven, relation of the horizontal limestones 

 of the Sao Francisco valley and of the Rio Una, which, for the present 

 at least, must be regarded as Palaeozoic and newer than the Espin- 

 hafo uplift. All things considered, it seems to me most probable 

 that the age, both of the rocks and of the uplift, will eventually 

 prove to be the middle or late Palaeozoic (Devonian to Permian). 



The escarped margins of the Serra do Espinhafo zone is in many 

 places very suggestive of faulting, and I was until recently inclined 

 to admit the existence of fault lines of gigantic proportions. With 

 a better knowledge of the adjacent regions, it seems probable that 

 this feature may be due in great part to denudation under conditions 

 of drainage and elevation different from the present ones. The 

 range throughout a considerable portion of its length is bordered 

 by well-defined denudation plains, some of which, as that of Joazeiro, 

 are but slightly sculptured, while others are dissected by valleys 

 excavated from 200 to 300"^ below the general level. In the region 

 of the middle Jequetinhonha the conditions at one time, probably 



