120 Mr. W. Phillips on Cleavelandite. [Feb. 



In all the instances above enumerated, and in many more in 

 which I have failed to discover the cleavelandite, it will b^ 

 understood that the means relied on for its detection were sim- 

 ply those of cleaving from the rock minute fragments, and sub- 

 mitting them to the reflective goniometer — a test it may be 

 assumed, sufficiently satisfactory, to render it needless to 

 have recourse to the labours of the chemist, where the 

 planes produced by cleavage are sufficiently bright, especially 

 since the angles at which the planes of the cleavelandite meet 

 each other are perfectly well ascertained, and essentially differ 

 from those of felspar, with which this mineral was always con- 

 founded, until the error was lately detected by the nearly simul- 

 taneous labours of Levy and Rose, and thereby furnishing 

 evidence (if indeed any were wanting) to the real value of the 

 mineralogical niceties belonging to cleavage and measurement, 

 and their essential importance to every one who would become 

 acquainted with the older rocks, which it may be said it is now 

 the fashion to neglect for the more inviting and less laborious 

 investigations requisite for the easier comprehension of the 

 newer. 



It is scarcely needful to say, that whenever felspar is men- 

 tioned as an ingredient of the before mentioned rocks, its pre- 

 sence was always ascertained by the goniometer. 



In several of the rocks of Mont Blanc and the neighbouring 

 mountains, it is however extremely difficult, if not impossible, to 

 decide whether one of their ingredients be felspar or cleavelan- 

 dite, without the assistance of the chemist, since the substance 

 in question is often either considerably granular, or approaches 

 the compact : sometimes, however, when that is the case, it 

 becomes manifest by a studious search that this appearance only 

 belongs to the cross fracture of the mineral, and that it does pos- 

 sess cleavages sufficiently distinct for the use of the goniometer ; 

 and in all cases where this has happened to me, the mineral has 

 proved to be cleavelandite, not felspar : in the specimen from the 

 Aiguille du Tour, which consists of a white granular substance 

 having some appearance of cleavage, and which is rendered 

 somewhat schistose by irregular layers of green chlorite, it is 

 impossible to decide on the nature of the white substance, 

 because the indications of cleavage are not sufficiently decisive 

 for the goniometer, but the examination of many rocks from the 

 neighbourhood leads to the conclusion that this substance is in 

 reality cleavelandite. 



If we regard the elements of the several substances constitut- 

 ing the rocks in which both felspar and cleavelandite occur, as 

 having been in a state either of aqueous solution or of igneous 

 fusion ; that is to say, in a state in which the two alkalies enter- 

 ing separately into the composition of these two minerals, were 

 at liberty to exert their affinities for other bodies, it seems very 



