80 



W. G. WOOLNOUGH. 



amount of departmental outfit to enable me to carry out 

 the investigation whose results are described in this paper. 



Main Geographical Features of the Area. 

 The Stirling Ranges form a unique feature in the geology 

 of Western Australia. The Ranges proper extend from a 

 point some two miles east of Oranbrook on the Great 

 Southern Railway in a general east-south-easterly direc- 

 tion for 44 miles, and terminate with extraordinary abrupt- 

 ness just to the east of Ellen Peak (about Lat. 34° 20' S. 

 Long. 118° 19' E.) They lie 42 miles north of Albany. 



The mountains rise abruptly from level plains, mostly 

 'sand plains,' which, with an average altitude of about 900 

 feet above sea-level, stretch far and wide in almost every 

 direction. To the north, as far as the eye can reach, even 

 from the highest summits, these plains continue without 

 interruption. To the west, at a distance of seven miles 

 west-south-west from Oranbrook, there is an isolated sugar- 

 loaf hill, Warriup Hill, which, though separated both 

 geographically and geologically from the main mass of the 

 Stirlings, is, nevertheless an outlier of the peculiar form- 

 ation which builds up the main range. 



Seventeen miles to the south, and facing the Stirlings 

 across the broad sand plain through which flows the Kalgan 

 River, lie the Porongrups, a range roughly parallel to, and 

 nearly as rugged as their northern neighbours, but absolutely 

 distinct in geological structure. Like the Stirlings, the 

 Porongrups lie chiefly to the east of the Great Southern 

 Railway, but Mount Barker and one or two other outlying 

 minor summits of the range extend westwards beyond the 

 line. There is, however, no considerable extent of high 

 land in this direction. From the high peaks at the western 

 end of the Stirling Range can be distinguished a number 

 of very distant summits lying in the region of the Lower 



