388 PROCEEDINGS OP SECTION C. 



of resisting atmospheric erosion which characterises the granite com- 

 pared with the sediments. Station Peak (1,154ft.), at the southern 

 end of the hills, is the highest point of the You Yangs and the level falls 

 to the north. The surrounding plain is at a low elevation. Lara and 

 Little River, the two railway stations nearest the hills, are only 52ft. and 

 108ft. respectivelv above sea-level. As a result, the steep-sided southern 

 end of the You Yangs, in spite of its comparatively low altitude, has, 

 as Professor Gregory remarks, (a) " all the impressiveness of a true 

 mountain." 



The Plain forms part of the large south-western plain of Victoria,, 

 extending from Melbourne on the east westwards through the Western 

 District. For the most part, near the You Yangs it is fairly levels 

 and is broken by only a few features. The Little River — a stream 

 draining the area north and east of the You Yangs- — has cut a gorge- 

 li'ke valley through the plain. On a smaller scale a stream called the 

 Duckponds, or Hovell's Creek, rising in the western part of the granite 

 hills, runs southwards in a similar steep-sided valley. Two or three 

 volcanic hills, from which part of the basalt of the plain has been 

 derived, rise above the general surface about seven or eight miles west 

 of Station Peak. Going westwards over the volcanic plain for about 

 five miles a ridge about 50ft. to 100ft. high, running west-north-west, 

 has to be surmounted. This proves to be the edge of a plateau of 

 similar volcanic rock to the plain below. The ridge may be due to 

 faulting before or during the volcanic eruptions, or the lava may have 

 flowed over a pre-existing escarpment. The plain, however, is not 

 entirely composed of basalt. Considerable irregularities of surface were 

 no doubt produced by continued erosion of the Ordovicians and of the 

 granite, and in the depressions in Mid-Kainozoic times freshwater lime- 

 stones were deposited. These contain freshwater shells, and are now 

 exposed in and near the valley of the Duck Ponds Creek. Later still 

 came the volcanic activity by which the basalt of the south-western 

 plains was poured out, filling up all irregularities of surface and, conse- 

 quently, varying greatly in thickness. The geological map also shows 

 some patches of older drift, consisting of ferruginous sandstones. Since 

 then a thin capping of a later superficial deposit has masked the basalt 

 over part of the area, and recent alluvium occupies the present stream 

 valleys and local depressions in the granite. 



THE GRANITE OF THE YOU YANGS. 



Effects of Erosion. — Outline- — The granite mass of the You Yangs, 

 viewed either from Lara or Little River, has at first the appearance of 

 the outline of stratified rocks, presenting a short steep slope on one 

 side, resembling an escarpment, and a long, gentle slope on the other, 

 resembling a dip slope. This appearance arises from the presence 

 of two sets of prominent joints which traverse the granite and determine 

 the nature of the outline produced by surface erosion, 



(a) " Geography of Victoria," p. 59. 



