19 



lacustrine def osit of tertiary age ; the former, an artificial 

 accumulation belonging to the existing period.* 



It may be well now to summarise some of the leading 

 features of the system with which, in detail, I have en- 

 deavoured to make you familiar. 



If in imagination we carry ourselves far back to the epoch 

 which immediately preceded the reign of the eucalypts, when 

 the Araucaria and Cinnamon trees graced the slopes of the 

 neighbouring hills, we might from some commanding eminence 

 (such as Mount Nelson) look down upon a magnificent sheet 

 of water at our feet which would, in a general way, resemble 

 in outline the existing estuary of the Derwent. With a few 

 minor exceptions its sinuous boundaries would follov^r the 

 same lines, but its waters would be fresh, and the Domain and 

 Trinity Hill would be almost isolated in their midst. The 

 great features of the surrounding country, Mount Wellington, 

 Mount Nelson, Knocklofty, The Gunner's Quoin, Mount 

 Direction, would be almost unchanged. On a stormy day we 

 might also see its surface broken into crested waves ; and in 

 the neighbourhood of One Tree Point and Geilston we might 

 watch how the chalky-looking cliffs of mudstone rock were 

 undermined and crushed by their repeated blows, and also 

 see the milky sediment the result of such waste as it was 

 floated away to eventually settle in the quieter waters of the 

 sheltering bays. 



The vegetation which luxuriously fringed its shores would 

 appear new, although its general features would not strike us 

 as being altogether unfamiliar. 



The botanist would find, instead of the sombre gum and 

 the green wattle, a large number of trees with elm-like leaves 

 and walnut-like fruits with 4 and 5 valves. In the slopes of the 

 bay near Geilston a species of Araucaria (A. Johnstonii), like 

 A. Cumiinghami, would rear its curiously imbricated branches 

 crowned with their singular spiny cones. If we searched 

 among the dead wood in the shady places we should find an 

 abundance of strange land shells (Helix Huxleyana, H. 

 Geilstonensis, Bulimus Gunnii), one of which a larger species 

 (Helix Tasmaniensis) would be specially interesting in the 

 eyes of a conchologist. At times our imaginary conchologist 

 might espie, however, a single individual whom he would 

 recognise as an old acquaintance (Helix Sinclairi). It is even 

 possible that no fresh-water Unio would be found to inhabit 

 the waters of the lake ; and thus it would exhibit a similar 

 relation to that which at present distinguishes the northern 



* Having examined a number of the shell heaps near Hobart, I have no 

 doubt whatever of their aitificial character. They resemble shell heaps 

 that I have seen along the Atlantic and Pacific Coasts of America, which 

 were deposited by the Indians living on the coasts. — W. Denton. 



