GcoJor/1/ of NillaJi cootie. 289 



about 850ft.. and clinibin<r upwards alono; the sui'veyed road to 

 Mt. Samaria, these rocks are traversed until a height of 1100ft. 

 is reached, when granite porphyry makes its appearance. The 

 road passes along over this till, at a height of 1500ft., the 

 Silurian rocks reappear, but at 2400ft. ther give place to a 

 granite porphyry having a groundmass distinctly finer than the 

 previous occurrence, and the porphyritic felspars are much 

 smaller. On the final slope leading to Mt. Samaria, the prevail- 

 ing rocka are silurian sediments, but the denudation of these 

 frequenth' exposes the underlying porp'hyry, now passing to the 

 quartz porphyn' type. Finally at a height of 3138ft. above sea 

 level the summit of Mt. Samaria is found to consist entirely of 

 a quartz porphpy showing plienocrysts of quartz and felspar in a 

 fin&-grained groundmass. Th.e northern face of the mount is 

 extremely precipitous, and an imperfect columnar jointing in the 

 porphyry is to be observed. Extending in a north-easterly 

 direction from this point lies the main mass of the porphyry 

 forming the TonmbuUup and Tolmie Highlands. 



On the western side of the river the gi'anite rises to some 

 hundreds of fee^^ above the level of the river. Porphyry occurs 

 also on the Strathbogie side, but this area haiS not been exam- 

 ined, so that the junction of the two types is not known. 



(C). — The Conglomerate. 



The best development of the conglomerate is met with below 

 the junction of Back Creek and the Broken River, whc're it 

 reaches a width of 50 chains and is up to 70ft. in thickness. The 

 conglomerate consists of boulders and pebbles of all sizes, set in 

 a fine graned material, the boulders consisting of quartzite, 

 hornfels, indurated mudstone, shales, quartz, granite, granite 

 porphjTy, aplite, tourmaline aplite, quartz porphyry, etc. Tlie 

 general size of the boulders is from 1ft. down to an inch or twc^ 

 in diameter, the largest noted being in a small road cutting near 

 Back Creek, where a boulder of granite porphyry over 4ft. long 

 occurs alongside a mass of indurated mudstone a.bout 3ft. in 

 length. Many of the boulders are facetted and polished, but 

 striated boulders are rare, the few that were found not being 

 entirely satisfactory, so that the determination of the conglo- 

 merate as of glacial origin at present rests rather on its mode of 



20 



