00 ' THE TRAP FORMATION OF 



of aggregated particles of tlie same, will here and there be found, and this 

 it is which the native families pick out and work into lime. Where the grey- 

 coloured, large, rolled, and angular masses occur, there it is that a hornstone 

 and jasper is to be found, though not both together in the same spot. The 

 introduction of silica is of course the cause of the wholeness, and indura- 

 tion of those masses, which easily effervesce, but endless gradations are 

 to be seen between these, and the two other minerals just named. If in- 

 durated clay, and semi-formed jasper are the derivations, the colour of 

 these will, for the most part, be deep yellow ; if green earth is the consti- 

 tuent of a neighbouring amygdaloid, the specimens will offer two colours, 

 green and yellow, or yellow freckled with green. The hornstone varies 

 much, from deep chocolate to straw yellow, from flesh coloured to nearly 

 white. The flesh coloured hornstone, or chert, and the specimens shewing 

 the lime-stone passing into this flesh coloured hornstone, or chert, found 

 at Bapyle, about seven miles westward of Sugar, resemble exactly the 

 same substances brought from the lias of the Hattah district, or eastward 

 of Sdgar ; and this, together with the yellow fragments of lime-stone, of a 

 tooth-like form, and somewhat dendritic aspect, also found at Bapyle, as 

 well as elsewhere, is the fact that has much tended to increase the idea 

 that the lime-stone of the trap of Sdgar, and districts adjacent, is the 

 lower lias half calcined, and disguised by the trap. 



Some specimens of that v/hich I have called the characteristic lime- 

 stone will not effervesce at all, whilst others do so, but very weakly ; but 

 still oftener the acids take effect with sufficient briskness. Often the 

 stratum of lime-stone is broader than the trap, which reposes upon it, and 

 upon the mounds, and swells of lime-stone at the foot of the hills, occa- 

 sionally will be found, a spot solely occupied by innumerable small frag- 

 ments of spathose matter. These fragments are of a striated and radiat- 

 ed structure, and appear as if they had been purposely broken by the 



hand, 



