A Physical Description of the Island of Tasmania. 145 



crusted together so as to give them an almost vertical dip, and 

 lead to great mistakes as to their thickness, unless attention be 

 paid to the way the same strata are repeated in the various 

 folds. Above these are found the Devonian rocks. They 

 lie unconformably upon the Silurian strata, and though in 

 places they have been much disturbed, yet are, as a rule, not 

 so much inclined as the older system. Above these again 

 are found the carboniferous rocks, consisting of lower and 

 marine beds, as they are termed, and the upper or fresh- 

 water series. These beds do not lie comformably upon the 

 Devonian. They are nearly horizontal, but perceptible dips 

 can be observed where they are studied over large areas. 

 These beds are again succeeded by sandstones, called by 

 various names. The two formations do not pass quite con- 

 formably from one to another, and the line of division is 

 well marked. It is probable that these beds may be con- 

 sidered as Trias, or Lias, but this is of no moment just 

 now. Their age will depend upon the age ascribed to the 

 coal deposits of which so much has been written. Quite 

 conformably with these are the strata next in succession, 

 which are called the Wianamatta shales, which may be 

 Liassic. Certain sandstones of aerial origin next succeed, 

 whose true position is not yet decided. They lie above 

 the Cretaceous rocks in Queensland, and, possibly, those 

 of N. S. Wales (the Hawkesbury sandstone) may be older. 

 Associated with all these are igneous or metamorphic rocks, 

 called greenstones, or diorites. They are partly volcanic, 

 and partly, no doubt, ash beds, or dykes, but so altered that 

 we can only speculate generally upon their origin. But it 

 is clear that some are the most recent in age, for they have 

 broken through all the older formations, and in some cases 

 altered and disturbed them. They form a very large portion 

 of the rock system of the country. They overspread and 

 completely hide immense tracts of the underlying formations, 

 and sometimes, no doubt, they have broken them up and 

 destroyed them. 



Above the sandstones of aerial origin we find nothing of a 

 more recent age until we come to the tertiary drifts, tertiary 

 volcanic rocks, and recent alluvial deposits. These are more 

 or less well represented, but the tertiary volcanic rocks by far 

 the best of the three. Some very large tracts of country are 

 covered with very recent basaltic lavas, doleritic for the most 

 part, but evidently belonging to several periods of deposition. 

 On the southern and extreme northern portions of the chain 



M. 



