86 A. Heard — The Petrology of tlie Pennant Series. 



of an electro-magnet ; they had. an average diameter of about 

 O'l mm., and were soluble in hydrochloric acid. No nucleus of 

 quartz was observed after all action had ceased. When viewed 

 under the microscope in convergent light and between crossed 

 nicols, beautiful concentric and spheruJitic structures were presented; 

 these bodies show the black cross characteristic of radiate aggregates. 

 Other carbonates may have been present in isomorphous intergrowth 

 with the iron carbonate, but neither calcium nor magnesium was 

 detected by chemical tests. 



Cordierite. — Fairly fresh grains of this mineral were not abundant, 

 although some samples were found in practically every horizon 

 examined. The grains were irregular, but a few showed traces of a 

 short prismatic habit. The colourless crystals were easily 

 distinguished from quartz by means of their characteristic inclusions 

 of zircon and magnetite. Even the freshest grains showed the 

 beginning of an alteration to a greenish chloritic substance at the 

 edges or near the inclusions. The crystals were drawn out of a crop 

 of density greater than 2'9 by the electro-magnet. This slightly 

 magnetic character was probably due to the inclusions of magnetite, 

 which with those of zircon probably caused the density to be greater 

 than that of normal cordierite. 



Zircon was abundant in all horizons of the Pennants, occurring 

 in well-developed prismatic grains of an average size 0"15 by 0'05 mm. 

 Some of the crystals presented an almost perfect form, giving an 

 angle of approximately 48 degrees between prism and pyramid. 

 Many grains were slightly clouded, and showed a zonal structure, 

 a few of these were reddish and slightly magnetic, and may have 

 been xenotime. 



Eutile. — This mineral was present throughout the series in sub- 

 ordinate quantities. It generally occurs in the form of rounded 

 yellow or brownish-red grains, although colourless rutile has been 

 detected. Occasionally heart-shaped and geniculate twins were 

 observed. Rutile needles were found in the clays and shales, but 

 ^ot in the sandstones. Its extremely high refractive iadex, its 

 density, and its sub-metallic lustre, enabled this mineral to be 

 easily detected. A few of the red grains were slightly magnetic, 

 and were probably ferriferous. 



Muscovite was separated with difficulty by means of heavy 

 solutions, on account of the large surface area of the cleavage flakes, 

 which caused it to be distributed in all the crops. It was easily 

 separated by rolling the flakes down a rough paper tube, when the 

 mica cleavage flakes remained on the rough paper. Most of the 

 fragments showed some trace of hexagonal structure, .and were 

 either dark or gave low interference colours between crossed nicols. 

 Inclusions were frequently present. The secondary mica was in the 

 form of dense scaly aggregates. 



Pyrrhotite was found in relatively large quantities at almost 

 every horizon. The grains were irregular, and varied in colour from 



