Miner alorrical Notices. 501 



5 



sion of thin plates ooze out, each, of course, spreading some- 

 what short of its predecessor, but retaining the same form. 

 This is probably the mode of the formation of these crystals 

 of Galena, all of which bear the appearance of having under- 

 gone fusion. On many crystals of Fluor spar, from England, 

 successive plates of this kind may be observed ; many of 

 them, however, do not take their origin from the centre of 

 the plane. If these, like those of phosphate of lead, are 

 formed by the sudden cooling of heated solutions, this may 

 easily be accounted for on the assumption that one side of 

 the crystal was attached near the source of heat ; the other 

 side cooling more rapidly, the liquid inside oozed out nearer 

 the more heated and still soft edge or plane. The crystals 

 of phosphate of lead, on the contrary, cool equally on all 

 sides. Forms of quartz, with these plates, are quite common ; 

 and I have recently found crystals of phosphate of lime, from 

 Grafton, New Hampshire, with the same appearance. These 

 plates have been considered as marks of cleavage lines ; and 

 it is evident that the cooling of each plate, previous to the 

 superimposition of a fresh one, would cause less strength of ad- 

 hesion between them than between other lines of the crystal. 



PVROCHLORE. (Microlite.) 



The close examination of above 200 crystals, of the min- 

 eral named Microlite by Prof. Shepard, and the comparison 

 of them with about 50 crystals of Pyrochlore from the Swed- 

 ish localities, and from the Ural Mountains, resulting in their 

 agreement in color, cleavage, crystalhne form and modifica- 

 tions, indicated to me, in 1841, the complete identity of the 

 two minerals, although Wohler's analysis had decreed the 

 latter to be a titanate, while Shepard's had made the former 

 a columbate of lime. 



This identity, strenuously resisted by Prof. Shepard, al- 

 though on grounds which show a very superficial knowledge 

 of the whole subject, has been completely proved by subse- 

 quent analyses, particularly by that of A. A. Hayes, in Silli- 

 man's Journal, vol. xxxii. p. 341, and its station as a colum- 



