COEEESPONDENCE. 



141 



by lava iu its consolidation is full_y discussed. In a lava wlien cool- 

 iug there are centres of attraction more or less aflecting all the crys- 

 talline particles ; and in a uniform mass cooling throughout alike, 

 these centres would 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 

 spberes, 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." 



COEEESPONDENCE. 



On tlie Composition of a peculiar Suhsfance from the Wallabies^ Holes, 



River JSLurray. 



SiE, — In a recent number of ' The Geologist ' (Eebruary, 1862) ap- 

 peared the description and a sketch of a Tertiary limestone on the Eiver 

 Mm'ray, 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, E.G. S., for chemical examination. The result of my 

 analysis is as follows : — 



Bitunien and petroleum, with debris of mosses . , 40*57 



Sand and white mica 22*49 



Phosphate of ahiraina, with a little oxide of iron and phosphate of lime 6*42 



Carbonate of lime 30*52 



100 00 



