OBSERVATIONS WITH RESPECT TO THE 

 NATURE AND CLASSIFICATIOJS OF THE 

 TERTIARY ROCKS OF AUSTRALASIA. 



By R. M. Johnston, F.L.S. 



General Features of the Tertiary System. 



Overlying the prevailing sandstones, limestones, shales, 

 and coal beds of the Mesozoic Period are to be found vast 

 accumulations of clays, sands, gravel, marls, calcareous 

 grits, limestones, gypsum, and lignites, of either marine or 

 fresh-water origin. These accumulations, as a rule, do 

 not present the same features as those of the older rocks, 

 inasmuch as the process of consolidation and metamorphism, 

 excepting in rare instances, is far less complete. The 

 rocks generally are loose and incoherent, and their exposed 

 surfaces are less able to resist the weathering and denuding 

 influences of air and water. 



It is also manifest, from a study of these accumula- 

 tions in various countries, that for the most part they were 

 deposited within limited and comparatively shallow basins, 

 whether as sediments of fresh-water lakes, river beds, 

 estuaries, or seas. The frequent changes exhibited in the 

 order and composition of their beds also indicate that they 

 were often subjected to sudden changes of level, per- 

 mitting the same limited areas to be successively and 

 alternately invaded by the organisms of sea and land 

 within a comparatively short period of time. These 

 changes in some countries, as in France, America, Aus- 

 tralia, and Tasmania, are further greatly complicated by 

 widespread eruptions of basalts and associated tuffs, both 

 of which are often interstratified in thin regular sheets 

 over wide areas with the more common aqueous accumu- 

 lations of sand, clay, hgnite, marl, and pebble drifts. In 

 Australia, Tasmania, and also in Scotland (leaf-beds of 

 MuU) these basalts and their tuffs are most intimately 

 associated with leaf-beds. In Tasmania, notably at 

 Breadalbane, there is abundant evidence of the destruction 

 sub-aerially of perfect forests of conifers and angiosperms, 

 by vast outbursts of scoriae and volcanic dust, such as that 

 remarkable outburst which has recently buried and 



