24 The South Australian Naturalist. 



PETRIFIED REMAINS OF TREES. 



By A. G. Edquist. 



The red sands which extend from Plym]iton to the Grange 

 Pinery are the remains of a line of old sand dunes. These red 

 dunes were once white in colour, and appeared like the present 

 dune-formation bordering the sea. 



The Red Colour. — The red colour of the older dunes is due 

 to a film of iron oxide which surrounds each grain of sand. 

 Since their formation by the action of sea and water they have 

 drifted inland for a considerable distance, and in their advance 

 have completely covered and masked a stiJl older formation of 

 dune sandstone, lu one small area behind the Fulham rifle 

 range these older de])osits have been uncovered by the action of 

 the wind. 



An Ancient Flora. — At one time these last-mentioned sands, 

 now consolidated, presented an a])i)eai'ance similar to the 

 younger red sands that overlie them, and they were clothed 

 with trees and herbage. Of the nature of the trees it is difficult 

 to speak with certainty, but it cannot be gainsaid that trees did 

 grow there, for we may still see in situ the petrified stumps and 

 roots, telling their story with such dumb eloquence that no 

 doubt can exist in the minds of those who Avill pause and 

 consider. 



From Wood to Stone. — These ancient stumps and roots are 

 no longer of wood, but of carbonate of lime, or limestone, the 

 original wood having been completely replaced or calcified by 

 calcium carbonate. Whence came the carbonate of lime? Sea 

 sand is usually a mixture of quartz grains and finely broken 

 shell grit, which consists almost wholly of this lime carbonate. 

 Percolating rainwater dissolves the limestone and holds it in 

 solution. In dry weather the mineralised water rises to the 

 surface, and, on evaporating, leaves the lime behind, at or near 

 the surface of the ground. 



Travertine and Root-Moulds. — As this process is repeated 

 year after year, the accumulation of limestone increases until a 

 thick crust of white limestone, or travertine, appears, as we 

 see it in malice country. The formation of this limestone does 

 iiot xorevent the growth of trees, for so long as the vegetation 

 remains alive the limestone does not form a continuous sheet 

 nor encrust the roots. The expansion of the growing roots 

 cracks the limestone, and the C02 breathed out by the roots 

 produces carbonic acid, which dissolves the rocks immediately 

 in contact. Should the trees die, the mechanical action of the 



