90 
Journal of the 
micas analagous to the potass felspar, but containing, instead of 
that alkali, soda or lime. 
(b) . Hornblende in irregular crystalline masses, showing the 
usual prismatic cleavage and polychroism. 
(c) . Brown, highly-dichroic magnesia-iron mica. 
(</). Quartz filling in interspaces. 
(e). One of the most interesting constituents is, however, 
chlorite, which I observed especially in a slice taken from a 
sample from the Mt. Budgee mine. In this slice, while the general 
stiucture and composition were such as I have described, there 
was no hornblende, this constituent being represented by chlorite. 
It occupies just those situations which are in other samples filled 
by hornblende. It is in masses of fibrous plates, having ragged edges. 
When seen perpendicularly to the cleavage, it is almost colourless ; 
seen in the direction of the cleavage, it is slightly dichroic. With 
polarised light and crossed nicols, it behaves precisely as does the 
chlorite of the diorites of Swift's Creek. There are here, how¬ 
ever, no cases where any passage through alteration can be 
observed from hornblende to chlorite ; the alteration must be 
held to have been here completed, unless we conclude that the 
chlorite is an original constituent. I doubt this, more especially 
as this sample formed part of the “ footwall ” of the quartz lode. 
(/). In addition to the above, I note in these samples the 
occurrence of magnetite and pyrite, and, less frequently, of apatite. 
Conclusion .—The inferences to be drawn from the preceding 
statements are, I think, the following :—The dyke at Pretty Boy's 
Pinch and Granite Creek consists of ortlioclase and magnesia 
mica, and with amphibole and very subordinate triclinic felspars 
in the ground-mass. Its main feature is potass felspar in its 
monoclinic form, ampliibole and magnesia mica, and its structure 
is strongly porphyritic. It is therefore, according to the present 
classification, a porphyritic syenite, having affinities with a mica 
syenite (minette). 
The other dykes in the neighbourhood of Bulgoback are similar 
to each other ; they consist of triclinic felspars, hornblende, and a 
little magnesia mica, porphyritically dispersed in a microcrystalline 
ground-mass. Their mineral composition is that of the diorites ; 
their structure, however, being markedly porphyritic, places them 
among the hornblende porphyrites. 
