L'heiiti and Diabase Rocks. 241 



Tlie Diabases. 



The largest area of diabase occurs to the east and north-east 

 of Mt. Samaria, the highest point in the district. This area 

 is shown on the Geological Map of Victoria as belonging to the 

 older volcanic series, but is entirely dis^tinct from these rocks, 

 both in structure and occurrence. The diabase runs in a north- 

 westerly direction from a point about four miles north-west of 

 Hat Hill, and forms a hi^h ridsce along the western side of the 



O O D 



Holland's valley. This ridge rises to a height of 2700 ft., 

 above sea level, and is capped in places by a conglomerate con- 

 sisting mainly of pebbles of quartz and quartzite in a siliceous 

 cement. 



For some distance the Holland's Branch marks the junction 

 between the diabase and the Devonian porphpy, but near M. 

 Ford's allotment the rivc'r takes a fairly sharp turn to the 

 west, and cuts across the diabase and the continuation of the 

 ridge extends into the Parish of Toombullup, forming Bunning 

 Hill. The upper portion of Spring Creek runs along the westeim 

 boundary of the diabase, but near the junction of Spring Creek 

 and the Holland's Branch the diabase crosses the creek valley 

 and forms portions of the northern end of Blue Range, and 

 extends through this ridge into the valley of Samaria Creek. 



On tho other side of Samaria Creek, and only separated from 

 the main mass by alluvial Hats, are a series of low hills of 

 diabasio rocks, which occupy portions of allotments 65, 66, 70, 

 71, 72 and 73, Parish of Moorngag. 



Further to the north, in allotments 41, 42, 43, 44 and 45, dia- 

 basio rocks form a ridge running in a north-easterly direction, 

 the northern extension being overlain by cherty rocks. 



The Cherts. 



In the larger area of diabase numerous patches of meta- 

 morphic rocks are found, btit these seem to be detached blocks 

 resting on the sui'face of the igneous rocks, and are not defi- 

 nitely in situ, so that their relationship to the diabases is 

 extremely obscure. They consist partly of chert, but are more 

 chaleedonic than in the other areas. Jasperoid rocks and silici- 

 fied diabase artt also common. 



17 



