170 THE GEOLOGY OF THE CANOBOLAS MOUNTAINS, 



Canobolas; another, consisting of quartz-acmite-trachjte-porpliyry 

 (X.691) occurs on Portion 259, Parish of Waldegrave. Lastly, 

 what appears to be a large dyke occurs on the main divide south 

 of the Devil's Hole, and consists of an oligoclase-solvsbergite 

 (X.688); this outcrops again further to the east on Portion 171, 

 Parish of Waldegrave. 



(b) Necks. — Pings of solvsbergite, coarsely porphyritic, occur 

 on top of the Young Man Canobolas (X.686) and near the top of 

 The Pinnacle (X.691). These two plugs, as already mentioned, 

 probably represent the vents from which most of the melanocratic 

 types of trachyte were erupted. The only other plug observed 

 is that already described as occurring on top of the Old Man 

 Canobolas, from which the andesites were erupted. 



SOrder of Eruption. 



The order of eruption, judging from the field-evidence, was 

 from acidic to basic, as follows : — 



1. Comendites, pantellarites, and quartz-trachytes. 



2. Trachytes, and phonolitic-trachytes, with abundant tuffs. 



3. Andesite, somewhat basic in composition. 



4. Olivine melilite basalts. 



No great interval of time seems to have elapsed between the 

 eruptions of 1 and 2, and between 2 and 3. But between the 

 eruptions of 3 and 4, a long period of erosion is indicated, showing 

 a long lapse of time after the eruption of the andesite, before the 

 basalts were poured out. 



The volcanic history of the district was probably as follows: — 



Silurian — submarine eruptions, with the production of acid 

 rhyolites and rhyolite-tuffs. 



Devonian — none. 



Carhoniferous — intrusion of intermediate augite-porphyrites. 



Mesozoic — none. 



oce7ie I — outpouring of comendites, trachytes and andesites. 

 Aliocene ) ^ j 



Pliocene — fissure-eruptions, with outpouring of basic melilite- 



basalts. 



