A. Heard — The Petrology of tJte Pennant Series. 85 



abundant, in frayed and twisted laths. The felspars are so altered 

 that their exact species cannot be determined with certainty. Dark 

 mica is present in the form of a few frayed laths, which show but 

 little trace of alteration. Chlorite is abundant at every horizon. 

 Black opaque material is common and appears to be mostly 

 carbonaceous matter. Subangular fragments of shale are found 

 scattered throughout the series. Corundum has been detected in a 

 few slides. 



The Heavy Minerals. 



Specim.ens of the Pennant Sandstone from numerous localities 

 were crushed but not ground in a mortar, and were subsequently 

 jDlaced upon a series of sieves of mesh 30, 60, 90 to the inch, and well 

 shaken. Most of the heavy minerals passed the 90 mesh, especially 

 the zircon and rutile grains. 



The fine dust was removed by careful washing. The pounded 

 rock was not treated with hydrochloric acid before the heavy liquid 

 separation, as this destroyed many of the minerals. The crushed 

 rock was treated with heavy solutions in order to isolate groups of 

 minerals of known density. 



The following heavy solutions were used : — 



Sonstadt Solution, Specific Gravity = 2"6 

 Bromoform, ,, ,, = 2'9 



Sonstadt Solution, ,, ,, = 3"16 



Mercurous Nitrate ,, ,, = 4'3 



The bar-magnet and an electro-magnet with adjustable pole- 

 pieces were also utilized, and, after a little experience, it was seldom 

 found necessary to employ a heavy liquid with a S.G. greater than 

 2"9, except for the purpose of confirmatory tests. The use of simple 

 micro-chemical tests proved valuable in confirming the presence of 

 certain minerals. 



The grains, which were isolated by means of hand-picking under 

 a lens, were mounted either in clove oil (Refractive Index = 1'53) 

 or Canada Balsam for microscopic investigation. 



The following minerals were separated : — 



Siderite. — Moderately magnetic grains with S.Gr. greater than 

 3-16. These appeared yellowish in reflected light, and had a high 

 refractive index. Many of the grains were granular and contained 

 l^articles of carbonaceous matter. In warm hydrochloric acid these 

 fragments gave ofE an evolution of gas (CO2), and generally a minute 

 particle of angular silica was left behind after all action had ceased. 

 Much iron was found in the solution on testing. These grains 

 appeared to be free from calcite when the alum test was applied.^ 



Sphcerosiderite. — ^Numerous almost jDcrfectly rounded grains have 

 been placed in this group, distinct from that of siderite, on account 

 of their characteristic form. These bodies were drawn from 

 sei3aration of density greater than 3-18 and less than 4-3 by meana 



1 Weinschenk (Clark), Petrog. Methods, 1912, p. 151. 



