342 Froceedings of the Royal Society of Victoria. 



Rocks. 



From the base to the summit of Mt. Morgan, which at- 

 tained a height of 580 feet above the Dee River, igneousi rocks 

 predominate, and these constitute the country rock within 

 which is enclosed the large mass of siliceous material forming 

 the ore body. South of Mundic Creek is a very extensive tract 

 of course-grained horublendic igneous lock of unifoi-m character. 

 Higher \ip the western slope of the Mount, where the Rip and 

 Tear tunnels are, the rock appears to be a decomposed crystalline 

 igneous rock. On the soutli side of the Mount beds of volcanic 

 ejectamenta, including many fragments of red jasper, are exposed 

 near the New Reduction Works. Further up the spur, and 

 near the mouth of Freehold Tunnel, variolite occm*s. On the 

 east side of the Mount from Linda. Creek upwards crystalline 

 igneous rocks, such as diorite, syenite, etc., are exposed. On 

 the north side of the Mount a considerable area is occupied by 

 siliceous cavernous rock, from which sulphides have been re- 

 moved. It is doubtful whether the rocks resembling quartzite 

 met with in the tunnels, etc., are of ordinary sedimentary origin. 



The top of the Mount was occupied by, first, a core of soft red 

 sandstone horizontally laid down and much false-bedded, sur- 

 rounded by beds of loose sand, highly colom-ed with iron oxides 

 in part, and these again were surrounded by a belt of limonite 

 and beds of sand rich in iron oxides partly stained black from 

 the presence of manganese oxide. Almost entirely surrounding this 

 belt were the siliceous .skeleton rocks from which the sulphides had 

 been removed (Tufa of Dr. Jack's reports). Outside this 

 siliceous rock, and forming the walls of the mine, was an altered 

 igneous rock completely kaolinised, but in which the crystals of 

 felspar Avere still clearly discernible. This rock appears to be 

 an altered diorite. Cutting through the siliceous skeleton rock, 

 and also through the diorite walls of the mine are dykes that 

 also appear to have been originally of diorite, but that are 

 completely kaolinised at the surface. 



These dykes do not penetrate the loose sandy beds or the 

 limonite of the secondary ore, nor do they cut through tiie ^Desert 

 Sandstone core, for this is of still later age. 



1 Later research renders it improbable that these beds are of Desert Sandstone age. 



