15Y II. I. JENSEN. 859 



Mr. Rands considers the Tambourine basalt to be Miocene or 

 Pliocene, hence contemporaneous with many other Australian 

 basalts. The Mt. Mellum rock is, if anything, later. The com- 

 parative freshness of this readily decomposaVjle rock, the abund- 

 ance of vesicular basalt, which is ever so much more readily dis- 

 integrated than hard columnar basalt, are reasons which justify 

 us in assigning a late Tertiar}', Pliocene or Pleistocene, age to 

 Mt. Mellum. 



In his paper already cited, "^ Mr. Andrews looks upon the Glass 

 House Mountains as monad nocks, or hypabyssal masses left by 

 the denudation of a Tertiary (Miocene) plateau into which the 

 lavas had been injected. I cannot at present embrace that view, 

 inasmuch as tlie D'Aguilar Ptange appears from rri}^ observations 

 to be a Tertiary fold range, and not a remnant of a now-denuded 

 plateau. Besides, the petrographical nature of the Glass House 

 Mountain lavas and the occurrence of some tuffs in the ridge which 

 is here named Trachyte Range, indicate that the rock is volcanic 

 and not hypabyssal. 



The upper sandstones of the East Moreton may be in part of 

 Lower Cretaceous age, the Trias merging, as the Ipswich beds do, 

 into the Cretaceous. The absence of later beds in the district 

 can be explained on two hypotheses — either it has been dry land 

 ever since Upper Cretaceous times, or repeated fluctuations 

 causing periodical submergence have taken place. The latter 

 supposition seems more likely to be correct, accounting satis- 

 factorily for the aVjsence of cliffs, escarpments, and other signs of 

 great erosion. It seems the most natural conclusion to come to, 

 that moderately stable conditions have prevailed in the Glass 

 House Mountains area ever since the trachyte eruptions, and 

 that the district has preserved its character as a low-lying coastal 

 plain, occasionally submerged, but each period of elevation 

 sufficing to remove the deposits formed in the period of sedi- 

 mentation. 



* " Preliminary Xote on the Geology of the Queensland Coast." 



