272 W. E Hidden — Edisonite, a new mineral. 



and this would appear to be indicative of an accidental selec- 

 tion by the Platyceras for attachment to any particular crinoid, 

 rather than each crinoidal species possessing its own particular 

 species of Platyceras. The latter case would be suggestive of 

 the Platyceras being more or less parasitic in its habits, which 

 in reality it doubtless was not. 



Art. XXYIII. — On Edisonite, a fourth form of Titanic acid ; 

 by W. E. Hidden. 



The original specimen of the mineral here described was 

 discovered by the writer in the summer of 1879, at the Whist- 

 nant Gold Mine, in Polk County, North Carolina. It was 

 found in the concentrations of placer washings and was asso- 

 ciated with gold and well-preserved crystals of zircon, xeno- 

 time, monazite, rutile and a dozen or more commoner min- 

 eral species. The orthorhombic symmetry of the mineral was 

 early noticed, but I was unable to decide which direction to 

 make the vertical axis of the crystal. Kef erring to my note- 

 book I find two sketches made from this specimen. Figures 

 1 and 2 are copies made from .these drawings. The angles I 

 then obtained were unsatisfactory, being made with a hand 

 goniometer, yet they served to prove the orthorhombic char- 

 acter of the crystal ; these angles are given below. The other 

 characters of the mineral noted are as follows : Cleavages par- 

 allel to three forms or six cleavage planes in all. Fracture 

 small conchoidal. Hardness about 6 (scratches glass); specific 

 gravity =4*26. Luster resinous to adamantine. Color bronze- 

 yellow to golden brown. Streak yellowish white. Insoluble 

 in acids. Unchanged before the blowpipe with soda; but 

 with borax gives a brownish bead much like the color of the 

 original mineral. 



The above comprises all the results obtained on the specimen 

 up to 1886, when I sent part of it to Professor DesCloizeaux, 

 for careful measurement of angles and chemical examination. 

 A letter from him, dated May 8th, 1886, contained the fol- 

 lowing information : 



" .... In regard to the ' unknown substance,' after having 

 made a careful examination I have found, with a new objec- 

 tive and a new illuminator of the Bertrand microscope, that 

 the mineral has but a single optic axis, or two axes extremely 

 close, with bisectrix perpendicular to the acute edge of 40°. 

 This edge shows one positive axis with cross divided with 

 difficulty. My friend Damour, so skillful in determining small 

 quantities, can only find titanic acid. Therefore, on account of 

 the easy cleavages following a-J, less easy it seems to me than 



