•92 



W. G. WOOLNOUGH. 



have suffered induration. At a distance of about twenty 

 yards from the contact the slates have been converted into 

 a thoroughly recrystallised hornstone, a type of alteration 

 completely distinct from the regional metamorphism into 

 phyllites which occurs to such a large extent in the eastern 

 section of the range. In the slate quarry, two hundred 

 yards from the contact, the rocks are lustrous purple slates 

 with a very perfect cleavage striking 23° west of north, 

 and therefore nearly parallel to the general trend of the 

 junction line. This cleavage stands vertically; cross joints 

 clip north 28° west at 50°. At a point ten chains south- 

 west of the quarry a tongue of quartz-porphyry intrudes 

 the quartzite. There is thus no shadow of doubt as to the 

 relative ages of, at all events some of the granites, and the 

 Stirling Range Series. 



Considering the great frequency of basic dykes through 

 the gneissic granite in the areas surrounding the Stirling 

 Ranges, the scarcity of such dykes cutting the sediments 

 is conspicuous* Throughout the length and breadth of the 

 range only one basic dyke was definitely located. There is 

 one of very considerable magnitude (about 18 feet wide), 

 which crosses the ridge of Toolbrunup immediately to the 

 west of the highest summit and gives rise to the depression 

 which separates this peak from the western summit. The 

 steep talus slope which forms the best means of* access to 

 the summit is composed to a notable extent of material 

 from this dyke. While the presence of the eruptive rock 

 can be traced from a distance on both slopes of Toolbrunup 

 by reason of the brighter colour of the vegetation growing 

 on it, no indication of its continuation was noted on the 

 plains either to the north or the south. The rock of this 

 dyke is rather coarse grained ophitic quartz-dolerite in 

 which a good deal of the pyroxene has been altered to 

 fibrous green uralite. It is therefore of a type which is 

 extremely wide spread in Western Australia. 



