BY H. I. .lENSEN. 99 



sections abundant. Some oligoclase crystals are nicely zoned. 

 Optical zoning is most prevalent. Some are mechanically zoned, 

 and outside the dusty zone of inclusions there is a border of anor- 

 thoclase. In one corner of the slide is seen an aggregate of large 

 oligoclase phenocrysts which, in unpoiarised light, appear a homo- 

 geneous mass of felspar studded with inclusions of iron-ore and 

 decomposition-products, but which, between crossed nicols, is 

 resolved into a cluster (xenolith of the same magma). Its 

 appearance is very like that described by me in these Proceedings 

 for 1907 (pp.611, 612, and Plate xxxii., fig.3). 



Acicular crystals of a variety of hornblende have been present, 

 but have only left their traces in masses of secondary magnetite. 

 A little ilmenite and primary magnetite are present. Apatite is 

 sparingly represented in minute needles. Kaolin and other dusty 

 decomposition-products are abundant, and secondary analcite 

 appears also to occur in the base. 



If the yellowish isotropic material be not all the result of 

 decomposition, a yellowish glassy base is present. 



Name : Andesite. 



Other specimens from the same spot are rich in specks of 

 chloritoids, allophane, and delessite of beautiful blue and green 

 colours. 



Soil : bhick and fertile. 



F1.25. Loc: dyke in trachyte-tuff near Anderson's, Little 

 Liverpool Eange. 



Fine-grained, greenish, aphanitic rock which has a greasy 

 lustre, and metallic ring like phonolite. 



Texture : holomicrocrystalline, porphyritic in a few microscopic, 

 rarely phaneric, phenocrysts; perpatic, with even-grained trachytic 

 base. 



Composition : the main constituent is felspar. The felspar 

 phenocrysts consist of an acid andesine in idioraorphic, sometimes 

 corroded phenocrysts. Carlsbad, albite, and pericline twinning 

 are shown. The habit of the phenocrysts is tabular. The 

 smaller felspar laths of the base consist of andesine, oligoclase, 

 and perhaps anorthoclase, showing Carlsbad or albite twinning. 

 Manebach twinning has been noted in some cases. 



