148 Chapman, Geological History of Australian Plants, [vofkxxv. 



A SKETCH OF THE GEOLOGICAL HISTORY OF AUS- 

 TRALIAN PLANTS: THE MESOZOIC FLORA. 



By Frederick Chapman, A.L.S., &c, Palaeontologist, National 

 Museum, Melbourne. 



{Read before the Field Naturalists 1 Club of Victoria, gth Dec, 191 8.) 



In continuing this sketch of the Australian fossil flora (a con- 

 tribution on the Palaeozoic flora having appeared in Vict. Nat., 

 xxxiv., p. 140, January, 1918), we have seen how several of 

 the Upper Palaeozoic types of plant-life survived into Triassic 

 times. Some of these persisted as important components of 

 the succeeding floras of the Jurassic and even Cretaceous 

 periods. Thus, the ferns Cladophlebis and Tceniopteris, and 

 some conifers, as Araucarites and Brachyphyllum, ranged 

 throughout the Mesozoic system. This steady survival of so 

 many important plant types seems to indicate that the geo- 

 graphical conditions controlling this area of land-surface — a 

 legacy of the Gondwana-land period — did not suffer any great 

 disturbance during the period extending from the Trias to 

 Cretaceous inclusive. 



Lower Mesozoic. 



In commencing with the Triassic flora, we may note that 

 the sediments may best be studied in New South Wales, whilst, 

 for richness of plant-types, the Queensland Mesozoic beds 

 perhaps take pre-eminence. 



In New South Wales the Hawkesbury series comprises, in 

 ascending order — 1, Narrabeen Stage ; 2, Hawkesbury Stage ; 

 3, Wianamatta Stage. They consist of sands, shales, and con- 

 glomerates. These beds represent the sedimentation of a 

 vast area which was undergoing degradation, where shallow 

 lakes, sand-dunes, and local desert conditions formed the 

 prevailing features of the country. 



The Narrabeen Stage — with its Esther ia shales, cupriferous 

 shales, sandstones, conglomerates, and chocolate shales — 

 denotes an oscillatory series between brackish and fresh-water 

 conditions, as shown by the presence of ripple-marks, worm- 

 burrows, and sun-cracks. These conditions were not very 

 favourable for plant-life, excepting of a lowly kind, but the 

 remains of ferns would be brought down by swollen streams 

 acting on loosened soil. At Cremorne Point, Sydney Harbour,* 

 a bore which penetrated the Narrabeen beds proved them to 

 rest on the Newcastle Series (Carbopermian). At 620 feet 

 6 inches above this junction a series of sandstones, shales, and 

 conglomerates was found, 1,112 feet 6 inches in thickness, 



* J. E. Came, " Kerosene Shale Deposits of New South Wales," Mem. 

 Geol. Surv. N. S. Wales, Geol., No. 3., 1903, p. 141. 



