BY H. I. JENSEN, D.SC. 189 



belonging to this late geological age has been prepared by 

 Mr. E. C. Andrews. [1] 



It is the wTiter's opinion, as enunciated in' one of his 

 papers [29 (a)], that an arid climate was experienced in 

 Central Australia, immediately after the uplift of the 

 Cretaceous basin in the late Mesozoic and early Tertiary 

 times. During most of the Tertiary period, however, 

 conditions were extremely wet, a fact borne of it by the 

 sedimentary banding of clays and sands of fluviatUe and 

 lacustrine deposition, under the great Red Soil Plain, as 

 Avell as by the Black Soil Plains and gypsum beds. The 

 writer has had an opportunity to study these deposits 

 at Nyngan, on the eastern flank of the Cobar massive, as 

 well as on the western slopes of the Warrumbungles. 



The cause of the aridity of the Cretaceo- Eocene and the 

 present periods is undoubtedly, in part, a geographic one, 

 connected with the uplift of a girdle of tablelands round 

 the margin of the continent at the end of the Mesozoic, 

 and again at the close of the Tertiary period. Partly, too, 

 the cause is meteorological. During the two arid periods, 

 the climate of the Australian zone has been dominated 

 by entirely different atmospheric movements to those 

 prevailing in the Middle Tertiary. As shown in a paper 

 by the present AVTiter to this Society, it is likely that this 

 wet period and the Pleistocene glaciation of Kosciusko 

 was, in all probability, a cosmic one, the nature of which 

 is still doubtful, though it must be admitted that peculi- 

 arities in physical geography alone could have brought 

 about the result. 



The effect of Tertiary changes on the life of this con- 

 tinent have been most pronounced. 



The disappearance of the Cretaceous basin caused 

 a migration of those hardy forms of plant life, which had 

 developed on the barren soils of Western Australia into 

 the Eastern parts, where they expelled and subdued the 

 Indo-Malaysian type of flora. The latter has only succeeded 

 in maintaining its predominance on rich scrub soil in 

 leached basalt and alluvial areas. 



The invaders probably consisted of eucalyptus, 

 casuarinse, acacias, proteaceous plants, zamias, and epac- 

 ridese. The eucalyptus may possibly have originated 

 in south-eastern Australia, and this may also be the case 



