'264 OCCURRENCE OF UIATOMACEOUS EARTH, 



abundantly interstratified with rocks of the Desert Sandstone 

 ►Series, the age of which is Upper Cretaceous.* 



It is unhkely that these extensive eruptions took place in 

 Lower Cretaceous time, as that was a period of prolonged subsi- 

 dence, and Mr. R. L. Jack has commented on the fact that in 

 Queensland, at any rate, no lavas nor tuffs have as yet been 

 noted in the Rolling Downs Series (Lower Cretaceous). As 

 regards the downward limit in time of these eruptions, it is 

 improbable, therefore, that it was earlier than Upper Cretaceous. 



As regards the upward limit, the following considerations 

 suggest themselves : — It is improbable that the Warrumbungle 

 trachyte volcanoes, at the time they were active, were far distant 

 from the sea. They are now over 300 miles inland from the 

 Pacific, but during the Lower Cretaceous epoch the vv^aters of 

 the inland sea, which, at that time, must have extended from 

 the Gulf of Cai'pentaria to the Australian Bight, must very nearly 

 have washed the bases of the Warrumbungles. In Upper Creta- 

 ceous time elevation took place, and marine conditions were 

 largely replaced in Central Australia by shallow lacusti-ine con- 

 ditions. There is no evidence to show that marine conditions 

 obtained within a hundred miles of the Warrumbungles in 

 Tertiary time. On physical evidence therefore it might be 

 inferred that the age of the trachyte series might be placed at the 

 close of the Cretaceous, or at the commencement of the Eocene 

 periods. There is also some palteontological evidence in support 

 of this supposition, as will be stated in the next division of this 

 paper. 



III. — Details of the Diatomaceous Earth Deposit. 



The deposit makes two distinct outcrops at the bottom of the 

 shallow valley or gully through which flows Wantialable Creek. 



* "Geological Features and Mineral Resources of the Mackay District." 

 By A. G. Maitlanil. By Authority. Brisbane, 18S9. AUo see Geology 

 and Palsbontology of Queensland and Nuw Guinea. Jack & Etheridge, 

 Junr. Text. pp. 546-547. 1892. 



