ELISHA MITCHELL SCTENTIFIC SOCIETY. 63 



is jet black with occasionally a grayish crust. The form differs 

 from the zircous directly associated with them, and they are also 

 very much larger. Their black glassy fracture distinguishes 

 them from the fergusonite and samarskite of the same sands. 

 Their density equals 4.087. 



Cyrtolite (Hych^ous zirconium, etc., silicate). — Masses and 

 distinct crystals having curved faces and gray-brown color have 

 been met with at the Wiseman mica mine, in Mitchell countv, 

 associated with autunite, fergusonite and samarskite. Also at 

 Mill's mine, near Brindletown, and at the xenotime and poly- 

 crase (?) locality on the Davis land, near Green River, in Hen- 

 derson county. 



Thorite (Hydrous thorium-silicate). — The discovery of tho- 

 ria in the Burke county monazite* has led Penfieldf to regard 

 its presence as due to a mechanical mixture of thorite with 

 monazite. Dunnington suggested substantially the same after 

 an analysis of Virginia momizite.J Peufield states that "oxide 

 of thorium is widely different, in its chemical relations, to the 

 oxides of the cerium metals, and hence should not be present 

 as a replacement of them ; and moreover, as it is present in 

 very different amounts, it seems natural to assume that the tho- 

 ria exists in the form of an impurity." Penfield has shown by 

 a microscopic examination that thorite is present in monazite 

 beyond question. He prepared a thin section which showed 

 small grains of a darker resinous substance scattered through it. 

 It was moistened with hydrochloric acid, gently warmed, then 

 carefully washed with water and examined \vith the microscope. 

 Wl)ite blotches had taken the place of many of the resinous 

 spots, while the monazite appeared to be wholly unattacked. 

 This observation proved beyond doubt the (sometimes) inclusion 

 of thorite in monazite and substantiated the chemical evidence 

 (see analysis of monazite before noted). 



Now that thorite is known to exist in this State microscopi- 



*Edison found thoria in this mineral in 1879 in specimens collected by the writer. 

 TAm. Jour. Sci., October, 1882, p. 253. JAmer. Chem. Jour., IV, 138, 1882. 



