78 f Scientific Intelligence. 



iron and an undetermined mineral, rare. The most abundant and 

 characteristic of these species, andalusite, chiastolite, tourmaline 

 and corundum, are typical of schists (phyllites) altered hy contact 

 with eruptive rocks, and since the river Pedro Cubas flows mainly 

 over schists with frequent injections of granite, the association 

 suggests that the gold may be a contact mineral. In the wash- 

 ings from the sands of the main stream (Ribeira) these contact 

 minerals (except tourmaline) are entirely lacking and the most 

 abundant minerals are indicative of crystalline schists, with 

 probably, granite and syenite. 



In regard to the occurrence of the native iron, it is noted that 

 grains of the size of several millimeters are found. They are ir- 

 regular battered flakes with metallic luster, and strongly mag- 

 netic, that exposed to damp air soon become rusty. In order to 

 determine if these grains came from the iron instruments of the 

 old miners, gravel that was unquestionably virgin was extracted 

 with wooden instruments. The washing gave as great an abun- 

 dance of iron as those from the gravel heaps previously washed 

 by the old miners. 



Among the other notes, which include an account of pseudomor- 

 phous crystals of leucite in phonolyte, the occurrence of corundum 

 in Sao Paulo, etc., may be noted a description of phyllites with 

 ottrelite and magnetite from Sao Paxdo. In the zone of phyllites 

 traversed by the river Tiete, layers rich in ottrelite are met with 

 intercalated with others entirely free from this mineral. The 

 ottrelite is in discs or distinct hexagons of about 0*25 mm diameter. 

 Basal sections show distinct cleavage in two directions, making an 

 angle of 1 20° approx. Pleochroism tolerably strong between plum- 

 blue and olive-green. Angle of optical axes very small and the 

 inclination of the bisectrices to the vertical axis also small. In 

 the rectangular longitudinal sections pyramidal faces are occa- 

 sionally seen showing the crystals to be deformed hexagons. 

 Polysynthetic twins parallel to (001) and an hour-glass structure 

 shown by the arrangement of inclusions are almost constant. An 

 intergrowth according to the base of two individuals, one full of 

 twin lamella? and the other free from them was observed. In 

 another case the twins presented a wedge shape. Crossed and 

 contact twins according to one of the faces of the dome are also 

 common, the angle of inclination of the basal faces being between 

 110° and 125°. Similar twins are described by d'Achiarcli from 

 the Apuan Alps and are seen in jn'eparations from the Ardennes. 



Basal sections often show a distinct division into three rhombic 

 fields with extinction parallel to the diagonals of the rhombs. 

 As from its optical properties ottrelite is certainly monoclinic, 

 this twinning should be referred to that often observed in mica, 

 that is, twinning planes normal to the base (001) and parallel to 

 the edge (001): (110). 



In longitudinal sections the basal cleavage is very distinctly 

 indicated by lines parallel to the basal edges. A prismatic cleav : 

 age indicated by lines normal to the base is also distinct. Lines 



