GEOLOGICAL RECONNAISSANCE OF THE STIRLING RANGES. 93- 



Oq the eastern side of the summit of Ellen Peak is a deep 

 narrow grassy cleft about twelve feet wide, which cuts 

 through the rocks of the summit with the precision of a 

 knife edge. It bears 70° east of north. No eruptive rock 

 was seen, and the structure may be due to the widening 

 of a joint fissure. Its general appearance, however, is very 

 strongly suggestive of the cavity left by complete weather- 

 ing of a basic dyke though no "white trap" was noticed* 

 In the summit of Bluff Knoll there is a somewhat similar 

 cleft bearing 10° west of north, which is suggestive of a 

 dyke fissure. Here again, however, no trace of eruptive 

 rock was encountered. While, then, it is clearly evident 

 that the granite of Tenterden is younger than the Stirling 

 Range Beds, it would appear that the gneissic granites and 

 their associated basic dykes are, with few exceptions, older. 



Summary of Lithological Characters. 



The sediments are quartzites and slates with a slight 

 tendency for the former to predominate towards the base 

 and for the latter to be in excess at higher levels. The 

 sediments are not intensely altered for the most part: the 

 quartzites have suffered scarcely at all, while the slates 

 have been more profoundly metamorphosed. The extreme 

 is reached in "The Wedge" where quartz-schists and mica- 

 schists are developed. In general, alteration is greater in 

 the southern and eastern areas. In the former section 

 most of the slates have been converted into wavy phyllites 

 and considerable quartz injection has occurred. No trace 

 of fossils has been detected in spite of repeated and assidu- 

 ous search. At the western end the sediments are intruded 

 by granite, and at Toolbunup one considerable dyke of 

 quartz-dolerite was noted. 



Occurrence of Laterite. — That ubiquitous formation in 

 Western Australia, "laterite," is very scantily developed 

 in the area under consideration. The Darling Peneplain 



