SERRA DO ESPINHAQO, BRAZIL 397 



the region, or at least a typical portion of it, has been accurately 

 mapped, any attempt to determine its detailed structure is hopeless. 



The argillaceous members of the Minas series include micaceous 

 (mainly, if not exclusively, sericitic) schists, calc schists, graphitic 

 schists, chloritic schists, and talc schists. A considerable part, if not the 

 whole, of the last two types consists of undoubtedly sheared and meta- 

 morphosed eruptives, and I have elsewhere attempted to show (13, 

 14) that a part of the sericitic schists are of the same origin.^ There 

 can be no doubt, however, that the greater part of the series is of 

 sedimentary origin. Its age can only be guessed at, but it seems 

 tolerably certain that it cannot be younger than Cambrian, and that 

 it may be older. 



The Minas series has always been regarded as the characteristic 

 formation of the Serra do Espinhafo, and it is certain that it, or 

 another series very like it, appears throughout the entire length of 

 the range. To the northward of the Rio Doce section the charac- 

 teristic ferruginous and calcareous members seem to disappear in 

 the zone of the serra, though they occur again on the banks of the 

 Sao Francisco between Urubii and Joazeiro. It seems probable, 

 therefore, that more than one geological series is here included. It 

 is also certain that these characteristic members occur on both sides 

 of the Rio Doce section at considerable distances from the reputed 

 margins of the Serra do Espinhafo zone, and with indications of 

 folds with a northeasterly trend, and thus parallel with the neigh- 

 boring Archean ranges. It seems probable, therefore, that their first 

 and strongest folding was due to a movement producing northeast- 

 trending folds, and presumably involving the shale, sandstone, and 

 limestone series of the Sao Francisco basin as well. The occurrence 

 farther southward in the Parana basin of a series very similar to this 

 last, and which has been involved in the northeast folds of the adja- 

 cent Archean region, confirms this point of view. These rocks of 

 the Parana basin, like those of the Sao Francisco, are in general but 

 slightly metamorphosed and are overlain, in the state of Parana, by 

 horizontal strata containing Devonian fossils (15), Though they 



1 Since the above-cited papers were written, a specimen has come to hand showing 

 one of the types there discussed (the monazite-bearing schist of Sao Joao da Chapada), 

 with a 'vyell-defined eruptive contact with quartzite. 



