140 ORVILLE A. DERBY 



cations point to an original bed of sandy ferruginous shale 

 rather than to a vein. 



The third body, not seen by me, is, according to both Bur- 

 ton and Grociex, characterized by a white feldspathic clay, 

 kaolin, or lithomarge, with crystals of quartz and specular iron. 

 Specimens exactly corresponding to this description were kindly 

 furnished by Dr. Thomassi Bezzi, who collected them with the 

 assistance of the owner of the mine, so that their authenticity is 

 undoubted. Two specimens representing the Barro and the 

 Duro mines are practically identical. In both a mass of snow- 

 white, structureless clay, with nests of quartz crystals and spec- 

 ular iron, has adhering to it colored laminated clays. The 

 contact between the two, sharply defined by the strongly con- 

 trasted coloration, is in part linear, in part irregularly undulated, 

 but without appearance of graduation from one to the other. 

 Irregular stringers of the white clay penetrate the mass of the 

 colored, and irregular masses of the latter are inclosed on the 

 former. The whole appearance of the contact is that of a 

 vein or dike, represented by the white clay, with stringers and 

 inclusions of the country rock. The contrast between the heavy 

 residues of the two kinds of clay is as striking as that of their 

 coloration and general appearance. Corresponding quantities 

 taken at a distance of a few millimeters from each other or either 

 side of the contact gave very different residues, both as regards 

 quantity and mineral composition. That of the white clay is 

 extremely small, consisting, aside from rare grains of quartz and 

 specular iron that apparently come from segregations rather 

 than from the body of the clay, exclusively of delicate needles 

 of yellow rutile, the Agulhas cor de ouro (golden needles) men- 

 tioned by Burton. The residue from the colored clay is, on the 

 contrary, abundant, consisting, after the separation of the quartz 

 (beautifully etched) and iron oxide, of rolled zircons, anatase, 

 tourmaline, and iron-stained earthy grains of rudely prismatic 

 form that evidently represent a decomposed silicate, possibly 

 staurolite. This last is a characteristic residue of a metamor- 

 phosed clastic rock, and as tourmaline and anatase seem to be 



