Intelligence and Miscellaneous Articles. 233 



their origin from the centre of the plane. If these, like those of 

 phosphate of lead, are formed by the sudden cooling of heated solu- 

 tions, 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 cry- 

 stals 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, pre- 

 vious to the superimposition of a fresh one, would cause less strength 

 of adhesion between them than between other lines of the crystal. 



Pyrochlore. (Microlite.) 



The close examination of above 200 crystals of the mineral named 

 microlite by Prof. Shepard, and the comparison of them with about 

 50 crystals of pyrochlore from the Swedish localities and from the 

 Ural Mountains, resulting in their agreement in colour, cleavage, 

 crystalline form and modifications, 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, although on 

 grounds which show a very superficial knowledge of the whole sub- 

 ject, has been completely proved by subsequent analyses, particu- 

 larly by that of A. A. Hayes, in Silliman's Journal, vol. xxxii. p. 341, 

 and its station as a columbate of lime, according to one of Shepard's 

 analyses, confirmed. Dana's Mineralogy, one of the arrangements 

 of which is crystallographical, although in the last edition entering 

 into every other possible detail on these two minerals, singularly 

 enough omits even an allusion to the above circumstance, notwith- 

 standing its being so remarkable an instance of the power of crystal- 

 lography to indicate error in chemical analysis, even in hands like 

 those of Wohler. 



This mineral is an excellent exemplification of the difliculties 

 which at present surround the natural arrangement of minerals, al- 

 though chemical analysis is unquestionably hereafter destined to 

 be its basis. The analyses of the dark- coloured crystals give as in- 

 gredients, Columbia acid, lime, manganese, iron, tin, lead, uranium, 

 &c. ; whereas the minute transparent yellow crystals are probably 

 pure columbate of lime, or, perhaps, even obtaining their colour from 

 a slight admixture of oxide of uranium, as this colour differs much 

 in intensity in crystals of the same size. These small transparent 

 crystals are generally modified on the edges and soHd angles of the 

 octahedron; in the large dark- coloured crystals these modifications 

 are often nearly obliterated. 



My largest crystal of pyrochlore, from the Chesterfield locality, is 

 three-eighths of an inch at the base of the octahedral pyramid. 



Columbite is usually described as of a dark, opake, sub-metallic, 

 iron-black colour. I possess a small crystal of this substanoe, from 



