MENACANE, 



137 



GEOGNOSTIC OCCtJRRENCE. 



This fossil has hitherto been only found, accompanied Geognostlc 

 by fine quartz sand, in the bed of a rivulet, which washes ^'^'^"'^''^^ 

 the valley of Menachan, in Cornwall. The neighbouring 

 mountains belong to the primitive order, in which, most 

 probably, the mcnacanc formerly constituted a superficial 

 layer ; but, by their decomposition, and consequent degra- 

 dation, by means of rains and floods, the earthy parts hare 

 been carried off, and the heavier metallic fragments collected 

 in the valley. 



FIFTH SPECIES. Species V. 



Isermc, 

 ISERINE. 



Iscrine of Werner. 



EXTERNAL CHARACTERS. 



The colour is iron black, inclining a little to brownish External cha» 

 black. Is found in small obtuse, angular grains, and in '■*<^'^'''' 

 pebbles, with a Somewhat rough, strongly glimmering surface. 

 Internally, it is shining, with semi-metallic lustre. Frac- 

 ture is more or less perfectly conchoidal. Fragments are 

 indefinitely angular, and sharp-edged. Perfectly opaque. 

 Hard. Brittle. Retains its colour in the streak. Is heavy, 

 in a moderate degree (4,500). 



OBSERVATIONS. 



Of all fossils, this has the strongest resemblance to Iron observatiooi 

 sand ; into whJch, as Mr. Werner first observed, it actually onlserinc. 

 graduates, but may be distinguished from it by the shade 

 of brown in its colour ; by its superior external, and in- 

 ferior internal lustre ; by its less specific gravity ; but, 

 chiefly, by being only slightly, and that by a powerful 

 magnet, attractable. From nigrine and menacane, it differs 

 sufficiently in fracture and lustre. This, as well as nigrine, 

 was first considered as a particular species by Werner ; both 

 which determinations were afterwards confirmed by the ana- 

 lysis. 



Vol.. XVI.— Feb. 1807. O CHEMICAL 



