The South Australian Naturalist. 25 



roots ceases to operate, and with the cessation of respiration 

 the production of carbonic acid stops. A crust of limestone at 

 once forms about the roots, and produces the root-moulds so 

 commonly found in the white dunes along- the shore. The trees 

 which gvevv in the ancient red sands were evidently smothered 

 by an invasion of the younger sand dunes. The strong- sea 

 breezes and j^revailing winds of summer caused the^loose rock 

 to drift inland, and in time to destroy the trees. As the buried 

 stems and roots decay, each tiny particle of wood is replaced 

 by a particle of limestone. 80 slowly and uniformly is the 

 ])rocess of substitution carried on that tlie radial structure or 

 grain of the wood is scarcely modified and still appears a well- 

 marked feature of the petriiied remains, or "fossil wood." 



The FincJ Phase. — Until recently the stumps were for the 

 most ])art standing erect just where they grew, but the hand of 

 time and of the unappreciative rabbiter has overturned most 

 of them, and the time is not far distant when the weathering 

 action of wind and rain will have reduced the last remnants to 

 dust. 



Work Still to be Done. — It may be possible for a field 

 naturalist, Avith a knoA\ledge of our timbers, to identify the 

 genus of the trees of whicli these fossils are the remains. They 

 may represent the native ])ine (Callitris), or the sheaoak (Casu- 

 arina), for both these trees grow at the present time in the 

 locality, in sands which must eventually take on the appearance 

 of this older rock. 



NOTE ON ANTS AND FROGHOPPERS. 



By Albert H. Slston, F.E.S. 



Ants are, perhaps, the most interesting of all insects, and 

 much has been written about their habits and social life, and of 

 the inquilines that inhabit their nests. J. H. Fabre. in his 

 "Social Life of the Insect \Yorld," writes of ants and other 

 insects that obtain the sap from the hole made in the tree by 

 the rostrum of the Cigale (Cicada), and I shall now briefly 

 relate hovr ants feed, indirectly, upon the sap of the tree. 



This operation may be witnessed during the spring and early 

 summer months on Eucalyptus saplings and on gum trees that 

 have been cut down and sprouted again. Pick out a tree that 

 is swarming vrith ants, and you will probably find a number of 

 the froghopper larva? feeding upon it ; they will very seldom be 

 found alone, but in the company of one or more ants, vrho are 

 busily at work milking, in their ovrn way, their "cows," 



