200 TERTIARY ROCKS OF AUSTRAJLASIA, 



continuity of land and freshwater deposits from the 

 Mesozoic period to the present time. As we cannot, there- 

 fore, look for any limit corresponding to a complete strati- 

 graphic break, and as no contemporaneous fossil organisms 

 have yet been found which would help us to fix the 

 character of the various beds, the evidence as to their age 

 must be based upon the nature of their position in relation 

 to altitude,' superposition, and particularly to the earlier 

 signs of erosion of existing lake-basins, valleys, and water- 

 courses (500 to 700 feet above existing channels) through- 

 out Tasmania. Among the more important of these 

 deposits may be noted the gravelly and gritty accumula- 

 tions forming the older terraces overlying the Archaean 

 and Silurian formations of the western part of Tasmania, 

 and more particularly the older gravel drift terraces of the 

 600 to 700 feet level forming the upper zone of the 

 Launceston Tertiary Basin, occupying nearly the whole of 

 the rolling plains drained by the Tamar and its important 

 tributaries. Fine sections of these older INeogene drifts 

 are to be seen in the neighbourhood of Breadalbane, 

 Perth, and Longford. 



Where there are elevated plains composed of lignites, 

 leaf-beds, clays, or older basalts in ascending order, and 

 where these, again, are immediately succeeded by sand- 

 stones, pebble drifts, and conglomerat-es, we may with 

 some degree of confidence separate the latter from similar 

 deposits formed by erosion of the older formations, and 

 redistributed along the lower levels of the broad valleys, 

 now in places cut to a depth of more than 500 feet below 

 the levels of the ancient lakes and watercourses. Forma- 

 tions, often of great thickness, fringing the shores of 

 Macquarie Harbour, and occurring in the neighbourhood 

 of Port Davey, Pieman Biver, and Long Plains, afford 

 similar evidence. Between the Arthur Ranges and the 

 parallel channel of the Upper Huon similar elevated 

 terraces, with deeply cut cross valleys eroded by old or 

 "existing tributaries, also afford evidence of the great extent 

 of formations accumulated during the Neogene period. 



The older gravel drifts, sometimes 70 feet above the 

 more recent alluvial fiats bordering the River Derwent, 

 and forming terraces flanking the mud stones of Upper 

 Palaeozoic age, are also no doubt members of the Neogene 

 period. Evidences of a similar character in the north-east 



