Rocks with Quartz Veins in Brazil. 351 



the phyllites intercalated in the series in which the veins 

 occur. A large " horse " left standing in the center of Misael's 

 mine, and decomposed to a yellow ocherous clay, shows to the 

 naked eye abundant pyrite (altered to limonite) and tourmaline, 

 and affords on washing a very slight residue of quartz, much 

 tourmaline in handsome prisms, and a comparative abundance 

 of well-rolled zircons with rare grains of rolled rutile and still 

 rarer ones of sagenite that, like the tourmaline, appear to be authi- 

 genetic. An ash-colored clay poorly exposed, only a few meters 

 away and of very similar aspect, affords an entirely different 

 residue characterized by an extraordinary abundance of minute 

 sharp-angled prisms of monazite of peculiar type, with rare tour- 

 maline and still rarer octahedral xenotimes often intergrown with 

 zircon but altered to a yellowish mass that is difficultly distin- 

 guishable from the aggregates of titanium minerals so abundant 

 in the various rocks of the region. There is here a complete ab- 

 sence of rolled zircon or of other elements that can be considered 

 as allothigenetic. Specimens from two distinct outcrops of the 

 green schist associated with quartz veins in the immediate 

 vicinity of the mine show, along with much rutile that is 

 evidently of secondary origin, a mixture of the characteristic 

 elements of the two clays above described, that is to say, per- 

 fectly sharp crystals of monazite with well rolled zircons, both 

 in considerable abundance. A polished cross-section of one of 

 the more massive pieces of this schist shows a banded structure 

 with alternations of a dark green with an ash-colored material. 

 The two are so intimately interlaminated that they could not 

 be completely isolated so as to give perfectly unmixed residues, 

 but there is an evident concentration of monazite in the green 

 and of zircon in the lighter-colored portion. Thus both the 

 character of the residue and the aspect of the specimens indi- 

 cate that this schist has been produced by the shearing and 

 metamorphism of a mass of mixed material of which one part, 

 corresponding to the "horse" of the neighboring mine, is 

 characterized by allothigenetic zircons and the other, corre- 

 sponding to the other clay of the mine, by authigenetic monazite. 

 Thus the veins at Sopa appear to be highly-sheared bodies 

 essentially identical with the Gruia but more completely mingled 

 with the adjoining rocks. 



The observations above recorded indicate the presence in 

 the older series of the region of dikes of a rock characterized 

 by titanium minerals and monazite as primary accessories that 

 have been sheared and metamorphosed together with the rocks 

 into which they were injected, and that the schistose and pre- 

 sumably weak layers thus produced have more frequently than 

 others been the seat of subsequent injections of pegmatitic 

 material that passes to pure quartz. In the cases examined 



