192 VOLCANIC BOCKS OF SFRINOSURE. 



whole rock is microsphenilitic with very well defined perlitic 

 cracks through it {see Plate xii, fig. 3). There were no 

 traces of nosean crystals in this section. The specimen Avas 

 obtained from near the base of the How and is cvidentlj^ 

 a more glassy form of the phonoiite. 



At Dilly, which is aboiit five miles north of Springsure, 

 there is a pinnacle standing about 700 or 800 feet above the 

 surrounding basaltic country. The Avriter did not investi- 

 gate it but from the railway line it appears to be similar 

 material to the phonoiite on the Mountain and local inhabi- 

 tants state that it is of a similar nature. 



Dr. Jack* refers to a series of centres of eruptions or 

 " necks " standing about 300 to GOO feet above the level 

 of the old telegraph roatl between Springsure and Minerva 

 Creek.' He mentions Mt. Zamia, the Pigeon Hoiase, Saint 

 Peter and Little Saint Peter. He regards these necks as 

 composed of trachyte for the most part but some of them, 

 e.g. Red Hill, are partly filled up with a coarse angular 

 agglomerate in which basaltic fragments are mixed up with 

 the trachyte. Unfortimatelj', owing to limited time, the 

 author was unable to visit these points. 



Upper Volcanic Series. 



This consists of basaltic flows and just near Springsure 

 they are best developed on Mt. Boorambool. The flows are 

 horizontally disposed and there is a total thickness of about 

 600 feet. The thickness of individual flows ranges from 

 six to ten feet. 



Mt. Boorambool has a very well defined "' table -top " 

 appearance and to the west and couth, similarly-shaped, 

 flat-topped mesas may be seen. 



The weathering of the upper series of basaltic rocks 

 has resulted in several of these mesas being left where the 

 rocks have been more resistant ; the sharp breaking across 

 and comparatively steep sides of the ridges gives the table- 

 top effect. 



At Mount Boorambool there are several layers of rock 

 especially rich in hyalite which occurs in large masses. Some 

 of the flows are particularly rich in fayalite which on ex- 



*ABBtial Prog. Report, 1894, p. 9. 



