Derby.] 166 [Feb< 2 \, 



on gneiss, and are overlaid unconformably by Cretaceous deposits. The 

 metamorphism of the gneiss in this region was, therefore, early Palae- 

 ozoic or Archean. In the southern provinces, the evidence is more conclu- 

 sive. In Santa Catharina and Rio Grande do Sul, beds, whose Carbonifer- 

 ous age appears to he well proven, lie horizontally above inclined metamor- 

 phic heds. These Carboniferous deposits extend across the province of 

 Parana to the southern part of the province of Sao Paulo. Near Pont a 

 Grossa in Parana, Mr. Wagoner, assistant to the Geological Commission, 

 (bund, underneath the Carboniferous beds, others, also horizontal, contain- 

 ing Devonian fossils. In that region, therefore, we may refer the upheaval 

 and metamorphism to a period anterior to the Devonian, and probably, as 

 on the Amazonas, to one anterior to the Upper Silurian. 



We have seen that the metamorphic rx>cks present two distinct series, of 

 which one, consisting of crystalline rocks, was, with all probability, re- 

 ferred by Prof. Hartt to the Laurentian. It is probable that this series had 

 been metamorphosed and disturbed before the deposition of the second non- 

 crystalline series. It is true that there appears to be a concordance in 

 stratification between the two series, but it is by no means certain that this 

 concordance is perfect, and that the older series had not been disturbed 

 (probably in the same general direction), before the great general move- 

 ment of upheaval, which affected and gave character to the whole meta- 

 morphic region of Brazil, if not of the entire continent. 



In regard to the age of the second metamorphic series, we have by elimi- 

 nation reduced it to the ages intermediate between the Laurentian and the 

 Upper Silurian, that is to say, the Huronian and the Lower Silurian. It 

 seems probable that both are represented, and, accepting Prof. Hartt's sup- 

 position, that the rocks of the Tapajos are more ancient than those of the 

 Tocantins, we may provisionally refer those, with the felsites of the Trom- 

 betas, to the Huronian, and these to the Lower Silurian, a reference which 

 accords with another opinion of Prof. Hartt, that is, that the granular 

 quartzites (itacolumites) and talcose schists of Minas Geraes belong to the 

 Lower Silurian. 



At the end of this movement of upheaval and folding, the primitive 

 islands of Brazil and Guiana had received enormous additions to their 

 original areas, and extended to the limits already indicated, in treating of 

 the distribution of the metamorphic rocks, leaving between the two islands a 

 strait, some three or four degrees of latitude in width, in the narrowest part. 

 From that time, which was during, or at the end of, the Lower Silurian 

 commenced the proper history of the Amazonian valley. 



In this strait was deposited, without great oscillations of level or up- 

 heavals, comparable with those that had disturbed the metamorphic series, a 

 seriesof beds gently inclined from the margins towards the center, represent- 

 ing the formations from the Upper Silurian to the Cretaceous, inclusive. 

 There were, however, beforethe deposition of the Tertiary beds, considerable 

 eruptions of trap and diorite, and local disturbances in at least one region, 

 that of Erere. This region is so important in the study of the geology of 

 the Amazonas, as to merit special description. 



