112 R. A. Farquharson — Petrology of N. Kalgoorlie, 



evidences of shearing. Along the shear jjlaiies there has been some- 

 times a deposition of dendritic manganese oxide. The most important 

 feature about them, however, is the presence, particularly in 12331b, 

 of numerous irregular greenish patches, apparently embedded in 

 a keratophyre mass. These patches, which are soft, very minutely 

 scaly, and with a faint lustre, vary in size from i up to 1 inch in 

 length and breadth, and are generally, though not always, flattened 

 parallel to the line of shearing. They are much weathered, and 

 apparently consist wholly of minute scales of chlorite. Owing to their 

 presence, the rock has at first sight the appearance of a breccia, but 

 a careful examination of the material shows it to be without doubt 

 the keratophyre. 



The question arises as to what is the origin of the green fragmentary 

 forms. Both rock specimens were obtained from the same dump, biit 

 access to the shaft associated with it was impossible. An examination 

 of the dump, however, shows that from the one shaft there have been 

 thrown out both the porphyritic rock with the green forms and a very 

 much weathered soft-green schist. It proved impossible to obtain 

 anything like a fresh specimen of the latter, but from an examination 

 01 a slice of the most suitable material obtainable it was identifiable 

 as a fine-grained chlorite schist. Moreover, though all the rocks are 

 extremely weathered, there seems little doubt that the green 

 fragments and the chloritic schist are identical. Furtlier, the green 

 forms are all essentially of an angular nature ; they show no trace of 

 crystal outline, they are themselves schistose. 



Taking these facts in conjunction with the sheared nature of the 

 keratophyre 'matrix ', the most feasible interpretation of the occurrence 

 is undoubtedly that the green fragments are true xeuoliths. Owing 

 to the decomposed nature of the rock, however, the question is 

 a doubtful one. There is, of course, another interpretation, namely, 

 that the enclosures owe the circumstances of their occurrence to the 

 shearing of the keratophyre — that they have, in fact, been sheared 

 into it. It must be admitted that in no case does any assimilation of 

 the chloritic schist and the ' matrix ' seem to have taken place ; also 

 the majority of the enclosures appear flattened parallel to the plane 

 of shearing. On the other hand, in specimen 12237, in which the 

 shearing effect is not so pronounced as in 12331b, the enclosures are 

 sometimes only partially flattened, and in places appear to be nearly 

 normal to the shear plane. In addition, though there are numerous 

 green particles scattered through the rock, no granulation of the 

 larger xenoliths can be observed, and there is little drawing out of 

 the latter into lenticular forms. 



2. In Detail. 



The external characteristics have already been given. In some 

 of the freshest specimens green spots are visible which are not 

 referable to tourmaline, but which in section prove indisputably to be 

 chloritized phenocrysts of hornblende. 



■ Numerous determinations have previously been made of rocks more 

 or less identical with these, and such names as felspar-porphyry, 

 porphyrite, felspar-porphyrite, etc., have been given to them. 



