136 Geology of Hobart Town. 



now gathering upon the coasts both of Australia and Tas- 

 mania ; deposits which, in a future age, will probably be 

 entirely barren of fossils. Such beds would necessarily 

 present but few evidences of changes going on elsewhere, or 

 even of those taking place closely adjacent." If I may borrow 

 a simile, they will bear the same relation to fossiliferous strata 

 which the chronicles of a barbarous and uncivilised nation 

 will bear, to one wherein the arts of painting, sculpture, 

 and poetry are cultivated, and wherein a knowledge of 

 letters enabled the historian to chronicle and perpetuate the 

 events taking place around him. 



In speaking of the section passed over between Hobart 

 Town and New Norfolk, mention has been made of certain 

 " aqueous deposits." Among these, the most remarkable 

 feature is the enormous amount of pebbles accumulated in 

 many places.. Such peKbles are of every size, from that of 

 coarse grains of sand to boulders measuring several feet in 

 circumference. They are composed of a great variety of 

 materials : quartz-rock, granite, sandstone, limestone, basalt; 

 and diorite, and, in a few instances, what I judged to be 

 fragments of silurian slates. They are always waterworn to 

 a great extent. In some places, an accumulation of these 

 alone occupies the whole height of an exposed section, but 

 in most cases the pebbles are interstratified with a deposit 

 not unlike the Pleiocene drift of Victoria. 



One or two local geologists suggested that the phenomenon 

 might be due to glaciers once existing thereabouts. The 

 more likely cause would seem to be one involving tidal 

 action. The Derwent, as may be seen from the map, is of 

 very unequal widths in different portions of its course. Now 

 it contracts into a narrow channel, and anon it expands into 

 a wide lake-like basin. As may be supposed, this conforma- 

 tion, by the expansions acting as reservoirs, receiving, and 

 giving out, the tidal wave, is productive of currents running 

 with a rapidity quite sufficient to hurl onwards masses of 

 stone large as those in question. 



As the land rose from out the sea, it is probable that these 

 features were alternately enlarged or diminished, so that the 

 succession in the same spot of beds, apparently deposited 

 by slow and rapid currents, ?s amply accounted for. 



Some beds of shells, greatly resembling the estuary de- 

 posits around Port Phillip Bay, have lately excited consider- 

 able attention in Hobart Town : one party referring them to 

 the refuse left by the aborigines during their visits to the 





