ii cae 
do. not think this would account for the very 
THE HAWKESBURY SANDSTONE. 109 
; 
I agree with Mr. Tenison-Woods that the evidence as to ice 
action in the Hawkesbury rocks is not at present sufficient to 
warrant us in attributing the presence of the shale boulders to its” 
agency. It is true that I have not made a special study of glacial | 
os but I have examined many of them of various kinds in the. 
poets has become covered up with sand, and since consoli-_ 
The screes or accumulations of rock fragments which form 
at the base of cliffs, both inland and along the coast, are either 
and sands, or they may be covered up without losing their angu- 
larity of form, and the latter appears to have been the case in this 
1 ce. Subsequent investigation may however bring to light 
indisputable signs of ice agency. 
_ M.. Tenison-Woods speaks of the consolidation of the loose sand 
Into a solid rock by the mere dead weight and pressure of the sand 
above. Now I have no objection to take against this at all, for the 
elects of thousands of tons of pressure should have a very great de: 
todo in bringing about the consolidation of a mass of loose and 
Porous sand, but I think that the cementing material has played a 
much more important part. It has long been a very interesting 
question to me, but one which I have not yet had an opportunity 
to tackle, whether there is any appreciable difference between the 
Specific gravity of a rock taken from the surface and of another 
Portion of the same rock taken from a depth, ée., whether the 
ground down into rounded pebbles, giving rise to conglomerates 
hay been consolidated, and that the lighter uncemented portions 
Were drifted away by the wind, leaving a mass of stones behind ; 
He bottom. It is thus I offer to explain the widespre 
glomerates which we find lying on the coal formation, with very 
“es ster over thousands of square miles.” But I 
BY 
