174- A'. ('. Andre tea— The Geological History of the 



explain the existence of so many cosmopolitan forms of 

 xerophytic tendency which appear to have spread to the various 

 continents while yet these were all connected. Examples are 

 Acacia, Senecio, Lobelia, Campanula with Wahlenbergia, 



(hi'ijilidliiiiii. Helichrysum, and many others. Indeed the stu- 

 dent, of geography who has traveled widely feels the necessity 

 for postulating waste places, deserts and barren sandy areas, 

 even during the Cretaceous which was a period of base-leveling, 

 and of great spilling over of the ocean basins on to the conti- 

 nents. Sandy seashores must have existed as well as sandy 

 tracts of Triassic, Permian, and other rock types, and these 

 must have been relatively barren, while areas well-removed 

 from the sea in certain latitudes, would surely have been sub- 

 arid to arid as high mountain ranges were rare. Siliceous 

 sands whether along the seashore or inland must have produced 

 xerophytic growths even if subject to moist seasons. 



Nevertheless in the present report it has been thought advis- 

 able to emphasize the apparent zoning of climate both before 

 and after the isolation of Australia from the world generally. 



I. The Problem Stated. 



In Australia the flowering plants comprise from 10,000 

 to 11,000 species, distributed between about 150 families. 

 Eight small families are almost confined to Australia, namely 

 Goodeniacea?, CandolleaceEe, Brunoniacese, Casuarinacea?, Tre- 

 mandracese, Stackhousiacese, Philhydracese and Pittosporaceas 

 (with the exception of Pittosporum, which occurs throughout 

 the Old World tropics). 



Australia has an area of about 3,000,000 square miles, and 

 is composed mainly of a broad, low, western plateau, a low- 

 lying central area, a belt of plateau following the eastern and 

 southeastern periphery of the continent much like an intra- 

 marginal vein sympathises with the general curvature of the 

 leaf margin, and a narrow coastal strip in Eastern Australia. 

 The eastern plateau area is relatively narrow and relatively 

 high and is separated from the ocean by a well-watered coastal 

 area possessing a mild climate. To the coast the eastern 

 plateau, with a height varying from 1,700 to 7,000 feet, above 

 the sea, presents a rugged front dissected with profound gorges, 

 thiis forming a decided barrier locally to direct communication 

 between the inland and coastal plants. On the other hand 

 relatively-low gaps occur in the plateau masses and these per- 

 mit a moderate amount of communication between the coastal 



