398 ORVILLE A. DERBY 



have afforded no fossils, they are presumed to be of Cambrian or 

 Silurian age. 



This sedimentary series of the Parana basin is abundantly injected 

 with granite, which, for this region at least, fixes the age of the granitic 

 eruptions as pre-Devonian. The granites are of various types (horn- 

 blendic, biotitic, and muscovitic), and doubtless several periods of 

 eruption are represented among them, but presumably these were 

 contemporaneous with, or posterior to, the orogenetic movements 

 that produced the folding. The granites that occur quite abundantly 

 in the areas occupied by the Minas series have not been studied, 

 but it may be presumed that the above conclusions regarding age 

 and periods of eruption will apply to them as well. Aside from the 

 granites, these areas present frequent outcrops of basic eruptives of 

 gabbroitic, diabasic, and peridotitic types, which, so far as observed, 

 show signs of metamorphism (a certain amount of shearing and an 

 uralitic alteration of the pyroxene), which may plausibly be attrib- 

 uted to the later movement of upheaval that involved the overlying 

 sandstone as well. So far as observed, this last has not been ailected 

 by eruptive injections, nor do the auriferous veins so characteristic 

 of the Minas series extend into it. 



The sandstone capping of the Serra do Espinhafo zone presents, 

 everywhere that it has been examined, great uniformity of aspect, 

 except that the division into two series noted in the Paraguassu sec- 

 tion has not been observed elsewhere. The conglomeritic character 

 of the upper beds of this section is general throughout the range, 

 and although in the Jequetinhonha and Doce sections the rock is in 

 places somewhat metamorphosed, this apparently is not a sufficient 

 reason for considering it as distinct. Another very general charac- 

 teristic is the occurrence of diamonds, but these appear to be lacking, 

 at least in workable quantities, in the extreme southern portion of 

 the range in the vicinity of Ouro Preto, and also in the northern 

 portion in the Jacobina region and beyond.^ As already stated, 

 there are reasons for suspecting that the Jacobina sandstone is more 

 recent than that of the more southern portions of the range, but on 

 this head nothing definite can be said. As to whether, with this 



I The question of the mode of occurrence of the diamond in this range and other 

 parts of Brazil will be discussed elsewhere. 



