Mr. Levy on the Crystalline Forms of the Hay tor it e. 4-3 



that tint to the mass. It is shipped at Teignmouth, but for 

 what place I could not learn. This vein appeai'ed to me the 

 more worthy of notice, as being the only one I ever met with 

 of that substance. It is only about two miles from the vast 

 and extraordinary deposition of wood coal near Bovey, which 

 possibly might be advantageously employed in smelting it. 

 The vein of ironstone lies in slates, the killas of the Cornish 

 miner, but immediately reposes on a stratum of a substance 

 termed provincially Irestone (ironstone) from its excessive 

 hardness. It apjjears to be siliceous schist, and abounds so 

 greatly in some mines east of Truro in Cornwall, as to prove 

 greatly injurious to the miner. 



XIII. On the Origin of the Crystalline Forms of the Haytorite. 

 By A. Levy, Fsq. M.A. F.G.S.* 



"IVTR. W. PHILLIPS having been so good as to commu- 

 -'-'-'- nicate to me the drawings and measurements of the cry- 

 stals of Haytorite he has given in the preceding paper, I first 

 examined whether by taking a sufficient number of the ob- 

 served angles as data to determine the dimensions of the sim- 

 plest form which may be assumed as the primitive, the other 

 observed incidences did agree with the results of calculation of 

 simple decrements. Because if that was not the case (as no 

 doubt can be entertained on the accuracy of the observations) 

 it would follow, in the supposition of these crystals being 

 pseudomorphic, that they had not preserved exactly the 

 angles of the substance upon which they had been modelled. 

 Consequently no perfect agreement could be expected be- 

 tween the incidences they afford, and those of any mineral ; 

 and at the same time that it would make it difficult to decide 

 which was the substance they had replaced, a similarity of 

 their forms, and not too wide a difference of their angles, with 

 those of a crystallized species, would be sufficient to make it 

 probable that they were pseudomorphic crystals of it. In- 

 ferences entirely opposite to the preceding would be drawn, 

 if the equality between the observed and calculated angles 

 should obtain. 



Now the forms, and mere inspection of the ensemble of the 

 measurements of Haytorite prove, that we may assume for the 

 primitive form an oblique rhombic prism, the lateral planes 

 of which would correspond to the planes g ', and the base to 

 tlie plane /H (See the figures in the preceding paper); this 

 base being inclined upon the lateral planes at an angle very 



* C'omnninitated by the Author. 



G 2 little 



