of Lead ^ and on the Composition of Ozocerite. 389 



suggested a similar solution for a difficulty of a similar but 

 less striking character. At the same time it should be ob- 

 served that there is nothing in the idea itself of a bod}' as- 

 suming three or more incompatible forms which should in- 

 duce us to reject it. It is the absence of direct propf of the 

 fact which alone makes it prudent, in the present state of our 

 knowledge, to endeavour to explain away appearances such 

 as that presented by the group we are considering. 



We should however expect to find wolfram in the two 

 other forms, even if its own special form do not belong to the 

 group of simple tungstates, chromates, and molybdates. It 

 has indeed been met with frequently both at Huel Maudlin 

 in Cornwall, and Schonfeld in Saxony, in square prisms, 

 or octohedrons; but these have generally been considered 

 pseudomorphous, — as mere casts of former crystals of tungstate 

 of lime. I have not seen any of these crystals, and cannot 

 therefore judge of the evidence on which this opinion rests; 

 but as there appears no reason why wolfram should not in 

 favourable circumstances assume the form of the square prism, 

 it is not unworthy the attention of mineralogists to examine 

 how far these supposed pseudomorphous crystals are really 

 and always so, 



Durham, March 1838. 



Note, — Since the above paper was written I have seen 

 some of the octohedrons of wolfram from Huel Maudlin, and 

 externally many of them are perfect; internally, however, they 

 are often more or less hollow, exhibit no cleavage, but a 

 structure radiating from the surface inwards, while the in- 

 terior of the hollows is often studded with minute brilliant 

 terminal facets. These characters appear to justify the con- 

 clusion that they are pseudomorphous. Their interior cavity 

 would seem to imply that they are also epigene, and that, as 

 in the case of some of the Chessy malachites, the change has 

 commenced on the exterior of the original crystal. 



LXIV. On the Composition of certain Mineral Substances 

 of Organic Origin. By James F. W. Johnston, A.M., 

 F.R.SS. Lond, and Ed., F.G.S,, Professor of Chemistry and 

 Mineralogy, Durham.* 



HI. Ozocerite from Urpeth Colliery, near Newcastle-upon-Tyne. 



T^^HE attention of chemists and mineralogists has for several 

 ^ years past been drawn to a species of fossil wax found in 

 * Communicated by the Author. 



