98 Proceedings of the Royal Society of Victoria. 



the felspars of the rocks previously described from this aiea I 

 feel no hesitation in classing them as sanidine. Augite and 

 magnetite are present and also a small amount of some 

 secondary chloritic matter. 



About two miles east of the town of Coleraine, close to where 

 the Koroit Creek bends west, in a paddock belonging to Mr. W. 

 Young, occui-s a hard, dense, black rock of somewhat vitreous 

 lustre. As in the preceding rock, no porphyritic cr^'stals can 

 be noticed, but under the microscope it is seen to be made up 

 largely of felspar microliths showing well marked flow structure. 

 They do not, however, always give straight extinction. The 

 larger felspars are destitute of crystal boundary and appear 

 much eroded ; they are sometimes crushed and bent. On the 

 whole I am inclined to regard them as sanidine which has 

 through some physical agency had its characteristic properties 

 somewhat obscured. Augite and magnetite in grains are 

 distributed through the slide. With some diffidence I class this 

 rock — temporarily at least — as a trachyte. 



In other places near Coleraine — such as Den Hills and Nareen 

 — rocks somewhat similar to the one last described may be 

 found but in all cases they have undergone so much alteration 

 as to make their determination a matter of some uncertainty. 



It will be seen from this description of the Colei'aine trachytes 

 that though they present much diversity both of appearance and 

 structure, a regular passage may be traced from the dyke I'ock in 

 which the sanidine crystals are well developed to the specimen 

 from which phenocrysts of sanidine are absent and in which 

 felspar microliths formed the main part of the mass. It is not 

 clear from the field evidence that all these rocks of trachyte 

 type are of the same geological age but their petrological 

 characters seem to support this view. The discovery by Mr. 

 Denuant in the felspathic tufa on Mount Koroit, near Coleraine, 

 of small blocks containing a Mesozoic cycad — recognised by Mr. 

 Etheridge, junr,, as otozamites — may be held to show that, in 

 this part of the field at any rate, there is evidence of either later 

 or post-Mesozoic igneous activity. The field relations of the 

 volcanic cones, Adam and Eve, through which the tracliyte is 

 intrusive, suggest that these cones were possibly of submarine 

 origin, and that before extensive denudation had taken place 



