394 PROCEEDINGS OF SECTION C. 



to the Grange Burn close to its junction with Muddy Creek, which 

 is its last appearance to the south. Just opposite a cave on the 

 bank the bed of the Grange Burn is formed of short columns of 

 prismatic quartz-porphyry. It is a most picturesque spot, and a 

 favorite picnic resort for the residents of Hamilton, five miles^ 

 distant. 



VOLCANIC. See Plate XIV. 



The rocks which next come under consideration are perhaps the 

 most interesting in the whole area. Little notice has been hitherto 

 taken of them, and for convenience sake they are colored in the 

 geological map the same as those just described ; the two are, how- 

 ever, essentially different rocks. Owing partly perhaps to original 

 difference in composition, but also to the alteration and decom- 

 position which have taken place, there is much variation in the 

 appearance of the rocks now referred to. A few hand specimens 

 of a Coleraine rock have, 1 find, been classed as phonolite in the 

 Melbourne Technological Museum, but in geological descriptions 

 of the localities other names have been proposed, as basalt, green- 

 stone, diorite, &c. One of the ingredients of phonolite, viz.. 

 sanidine, shows in some of the rocks, but nepheline has not been 

 detected, and from a number of analyses made I conclude that it is 

 absent. 



At Carapook, Brit Brit, and Coleraine the rocks are fissile, and 

 split easily into flakes. In one locality near Coleraine some slabs 

 quarried for road metal emitted a ringing sound when struck by 

 the hammer. Near the surface the rocks are frequently decom- 

 posed, and even for road metal purposes rather deep quarries are 

 necessary. Ultimately they are converted entirely into kaolin, 

 sometimes gritty, and sometimes of a soft greasy texture. When 

 free from iron, which is often the case, it is quite white, and from 

 the last-mentioned variety small ornaments are made by residents. 

 At Wotong Vale, a few miles north of Coleraine, where the best 

 kaolin is found, a picturesque hill, called the Giant Rock, is little 

 more than a huge mass of kaolin. 



At Phoines, near Carapook, a green-colored rock shows, vmder 

 the microscope, clusters of small lath shaped, with occasionally 

 broader, crystals of felspar, which is probably sanidine. Accom- 

 panying them are numerous magnetite grains, and a brown-colored 

 mineral which suggests decomposed olivine. Fluxion structure is 

 noticeable in thin sections of this rock, as also in some pi-epared 

 from other varieties. 



In a quarry at the back of the Coleraine flour mill the surface 

 rock is white and highly decomposed, but lower down becomes 

 black, compact, and glistening. Under the microscope it is seen 

 to consist of a mass of sanidine crystals, with sharply cut boundaries,, 

 most of which are columnar-shaped, but some tabular. The 

 majority of the fonner, and all of the latter, are traversed by cracks,. 



