88 
Excursions. 
MAHOGANY CREEK — 2oth August, 1910. 
Leader, Mr. E. S. Simpson. 
Geology. — The ridges in the vicinity of the Mahogany Creek 
station are covered with a mantle of laterite several feet thick. 
A small portion of this was sufficiently rich in iron to have been 
used for flux at the Fremantle smelters some years ago. At 
present large quantities of more aluminous laterite are being sent 
to Perth for streets and footpaths. The party proceeded to the 
granite quarry about one mile south-east of the station. The 
scene of operations is a small boss of grey granite rising out of 
low lying sandy soil. This is the only granite outcrop seen in 
the vicinity. From the quarry paving blocks are made for use 
in street gutters in Perth. The granite is a somewhat fine 
grained rock composed of microcline, oligoclase and quartz in 
about equal proportions, together with a little biotite. Yeinlets 
of epidote are seen in some parts of the outcrop and a pegmatite 
vein about two feet wide crosses the boss almost in the centre. 
The pegmatite is composed of quartz and coarsely crystallised 
felspar, the latter being microcUne-perthite, i.e., microcline with 
narrow interlaminations of albite. A graphic intergrowth of 
microcline and quartz was also seen in parts of this vein. No rare 
minerals were seen. The writers’ experience is that these do not 
as a rule occur in the orthoclase or microcline pegmatite as- 
sociated with potash granites, such as those of Northampton or 
the Darling Ranges, but are almost invariably to be found in the 
albite pegmatites, associated with soda granites, such as are seen 
at Wodgina and Moolyella in the North-West or Ravensthorpe, 
in the south. 
Botany,-— For these notes I am indebted to Dr. Tratman. 
The season being so late this year, the flowers were not advanced, 
while many of them which had been in full bloom had again shut 
up their blossoms to avoid the cold air. Of orchids, the most 
conspicuous was the Diuris longifolia. It cannot be too much 
insisted upon that a botanical specimen of an orchid must include 
the whole of the parts under the ground. It will then be found 
that, so far as is now known, with one single exception, they 
have one or more distinctive underground tubers. The excep- 
tion is Diuris longifolia, which never has a bulb, but only a group 
of more or less tubeious fibres. This applies only to this one 
species of the genus, D. setacea and D. pauciflora having well 
marked tubers. Here is an interesting object of research for 
members— to find out whether Diuris longifolia is, in fact, the 
