COREESPONDENCE. 
141 
by lava in its consolidation is fully discussed. In a lava when cool- 
iug there are centres of attraction more or less affecting all the crys- 
talline particles ; and in a uniform mass cooling throughout alike, 
these centres \YOuld be equidistant and the contractile force equal. 
" In this case all the spheres of attraction would be equally similar 
in size and form, and would arrange themselves as closely as possible, 
that is, in the manner of the cells in a honeycomb, or as the circles 
in the figure below. 
" The fissures of retreat produced by the contractile force of all the 
spheres, acting contemporaneously, must evidently therefore divide 
the consolidated layer into hexagons, each straight fissure being tan- 
gential to the opposite spheres of attraction between which it is 
formed." 
COREESPO^s^DENCE. 
On the Composition of a peculiar Substance from the WaJlahies'' Holes, 
River Murray. 
Sib, — In a recent number of ' The Geologist ' (February, 1862) ap- 
peared the description and a sketch of a Tertiary limestone on the Kiver 
Murray, in Australia. In this limestone are a series of holes or warrens, 
inhabited by hosts of wallabies, kangaroo-rats, etc., and from these 
cavities there exudes a peculiar dark brown, sticky, odoriferous matter, in 
considerable quantities. This substance has been handed to me by 
Mr. Eupert Jones, F.G.S., for chemical examination. The result of my 
analysis is as follows : — 
Bitumen aud petroleum, with debris of mosses 40'57 
Sand and white mica 22"49 
Phosphate of alumina, with a little oxide of iron and phosphate of lime 6 42 
Carbonate of lime 30 52 
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