264 PETROLOGICAL NOTES, ii., 



6. Fine-grained gneiss, without phenocrysts. 



Perfect series of specimens can be collected in the quai'ry. 



The above facts lead me to advance the following hypothesis. 

 The gneisses of the Roelands District were produced from the 

 porphvritic granodiorite by uneven shearing processes, which 

 accompanied the injection of basic dykes, under intense pressure. 

 Earth-movement was prolonged after the intrusion of the dykes. 



The pegmatites appear to belong not to the granodiorite, but 

 to some neighbouring intrusive, perhaps the Collie granite, an 

 entirely.different rock. 



Physiogi'aphy. — The Darling Fault-Scarp has a more dissected 

 and mature aspect in the Roelands District than near Perth. 

 This is also expressed by the scarcity of laterite, and its retire- 

 ment from the edge of the range. This greater maturity is pro- 

 bably due to the heavier rainfall of the South-West. 



There is a marked contrast between the valley of the Collie 

 River west of Shenton Elbow, and that of the Brunswick. The 

 latter is more mature, meandering, and well filled with alluvial; 

 whereas, though the two are only three to five miles apart, the 

 former, though the larger, is a straight, V-shaped trench, with 

 more tributary gullies on the south than on the north. This 

 sugforests that the Collie follows a fault from Shenton Elbow to 

 the west, where it takes a sudden turn from its former course. 



The material from the Roelands quarry is being used for the 

 breakwater at Jiunbury, the quarry having been recently re- 

 opened. The quarry-face has now a very difiierent appearance 

 from what it had when I saw it last. 



The Crystalline Rocks of Albany. 



Previous observers have recorded only granites and basic 

 dykes from the old crystalline complex of Albany. A number 

 of different rocks occur there, however, and their relations are 

 clearly shown in many fine exposures. The following types have 

 been distinguished, and are arranged in order of increasing age — 



Basic dykes (two series). 



Pegmatites (two series). 



Aplite. 



