842 



THE GEOLOGY OF THE GLASS HOUSE MOUNTAINS 

 AND DISTRICT. 



By H. I. Jensen. 



(Plates xlvi.-l.) 

 Synopsis. 



PAGE 



i. Introduction ... ... ... ... ... ... ... ... 842 



ii. Bibliography ... ... ... ... .. ... ... ... 843 



iii. Physiography and Topography — 



{a) Undulating Sandy Country ... ... ... ... .. 845 



(b) The Glass House Mountains ... .. ... .. ... 847 



(c) Miscellaneous Notes on Physiography ... ... ... 848 



iv. Geology — 



(1) Structure and Origin of the Glass House Mountains .. 850 



(2) Order of Eruption of the Lavas ... ... ... ... 852 



(3) Occurrence of Dykes ... ... ... .... ... ... 852 



(4) Possible Laccolites 853 



(5) Occurrence of Tufaceous Rocks ... ... ... ... 854 



(6) Occurrence and Structure of the Andesite Formation ... 855 



(7) Occurrence of Columnar Structure ... ... ... ... 855 



(8) Occurrence of Basalts in the District ... ... ... 856 



(9) Situation of the Volcanic Rocks on Intersecting Groups of 



Cracks ... ... ... ... .. .. ... 857 



(10) Age and Origin of the Glass House Mountains and Adjacent 



Rocks 857 



V. Petrology .. 860 



vi. Other Austr.vlian Trachyte Areas ... .. .. ... 870 



vii. Miscellaneous Notes 872 



viii. Conclusion ... ... ... ... ... ... ... .. 874 



i. Introduction. 



T4ie Glass House Mountains form a group of conical heights, 

 scattered over a lenticular area whose centre is roughly forty-four 

 miles north of Brisbane, S, Queensland. In this paper it is 



