60 



of some large confused crystallization that had been in the 

 next strata. This hornstone, from specimens given me by 

 Lord Heathfield, has sometimes apparently very large green 

 octaedral fluor on it, covered with quartz crystals, and 

 some varieties of octaedral pyrites. The irregular fracture 

 of the former gives the matrix an odd appearance, some* 

 what resembling the ground plan of a fortification, and not 

 unlike what is called fortification agate, found on the Scot- 

 tish coast. The figure at the top of the plate shows the 

 octaedron and its cases. 



The lower figure is octaedral fluor, from Aberdeenshire. 

 I believe this maybe the first time it has been noticed*. 

 They are of a dark purple, but do not detach so freely as the 

 above : they are lighter purple or greenish on the inside, and 

 are heaped confusedly in a stratum of calcareous spar and 

 cawk, if I am not deceived. The figures at the bottom 

 are octaedrons lying on one of the faces, to show that the 

 fracture which is parallel to the face gives a hexangular 

 form, as expressed at the left-hand figure, and will account 

 for the hexaedral remains of the crystal in the figure. The 

 more triangular fractures are nearer the primitive faces. 



* Jameson c!r,ts not observe any thing more than that fluor has been 

 founc in Aberdeenshire. I think if he had seen acy octaedrons he would 

 have said " 



