42 PROCEEDINGS OF THE ROYAL SOCIETY OF QUEENSLAND. 
ground. Moreover, only about a fourth of the dyke outcrop has been 
tested with shafts ; and shallow rootings in the other portions show that 
phlogopite occurs right along it. 
Before leaving the subject of the phlogopite mine and dyke some 
interesting mineral associations should be mentioned. At the point 
where the dyke has been faulted, and a later pegmatite dyke has been 
intruded into the fault, there is a large development of phlogopite rock, 
and lenses of anthophyllite rock also occur. A large mass of phlogopite 
rock has also been developed on the hanging-wall side of the phlogopite- 
dyke north-west of the main workings adjoining a supposed aplite 
intrusion, and several others south-east of the main workings — also near 
supposed aplite intrusions'. Alteration of the gabbro to anthophyllite 
rock also occurs near the hanging-wall side south-east of the main shaft, 
and portions of the adjacent country rock here have been altered to 
aetinolite rock. The production of anthophyllite and actinolite is pro- 
bably due to fault movements, as these minerals occur in several sheared 
zones in basic rocks in other parts of the Hart’s and Strangway Ranges. 
Whatever may be the origin of phlogopite in other countries, pneuma- 
tolytic processes seem best to account for its presence in the Strangway 
Range. 
B. Muscovite. Considering the plentiful and wide distribution of 
muscovite in rocks, it seems a strange thing that the mineral is so scarce 
in large books. 
Muscovite is one of the major minerals in a considerable section of 
granite as well as of the gneisses and schists in the older formations 
throughout the world. 
In large crystals (called books, on account of cleavability of the 
crystals and flexibility of the sheets) it occurs only in coarse granitic 
dykes, known as pegmatites ; even in these rocks the mica books are 
sporadic, or in some cases confined to lenses within the dyke. 
It is only in those pegmatite dykes which invade the oldest gneisses 
and crystalline schists of the earth’s surface that sheet mica in com- 
mercial books is to be found. 
The Hart’s and Strangway Ranges (see plate I.) are, as described in 
my paper to this society last year, composed of Arcluean formations, 
consisting of gneisses, amphibolites, quartzites, schists, marbleised 
dolomitic limestones, and similar highly altered rocks 1 , traversed by 
thousands of pegmatite dykes. Most of the pegmatites contain only mica 
up to an inch or two wide in cross section, quite useless for cutting up 
into sheets. Many pegmatites contain very little mica at all. Some 
contain sporadic lenses rich in sheet mica. Very few of the dykes contain 
large mica books throughout the whole length of outcrop. 
These facts raise a number of important questions which are best 
dealt with separately. They are : — 
(a) What is the eause of the different nature of the granite- 
pegmatite dykes ? 
(&) What is the effect of the country rock on the dykes? 
(c) What are the indications by which a prospector should be 
guided in his search for commercial mica? 
