at Haytor, in Devonshire, 36S 



with, and in some specimens the prism is so shortened that 

 the pyramids appear to be nearly joined base to base. Co- 

 lumnar hexagonal prisms of opaque quartz are of frequent 

 occurrence, forming the nucleus, round which the other cry- 

 stals are often clustered, or stalactitic chalcedony deposited. 

 Of the transparent crystals, some are colourless ; of the rest, 

 the colours are ferruginous (this most common), clear topaz 

 yellow, dark red passing into black ; smoky brown (cairngorm) ; 

 various shades of purple, violet, or rose-pink (amethystine 

 quartz), and bright ruby red : these last are minute and very 

 perfectly formed crystals, lining cellular quartz. The finest 

 specimens of the amethystine quartz occur (very sparingly) in 

 geodes, in the loose head; the rest are found clustered in 

 rounded, reniform, or radiated masses, lining cavities, and in- 

 vesting and invested by chalcedony. 



Flint — In amorphous masses, and passing into chalcedony, 

 &c; the colours mostly ferruginous, or brownish black. 



Chalcedony — Passing into and also investing crystallized 

 quartz ; stalactitic (this occasionally incloses distinct globules 

 of water), mamillated, botryoidal, and lenticular. The prevail- 

 ing colours, various shades of ferruginous brown passing al- 

 most into black ; but occasionally, specimens are met with of 

 clear yellow ; pure milk-white, passing into pearly and trans- 

 lucent white ; caerulean, passing into peach-colour, and light 

 gray ; and fine plum-colour (the last from a bunch of manga- 

 nese). Frequently two or three successive coatings, some- 

 times of the same, sometimes of distinct colours, invest each 

 other, between each of which a thin lining of clay is often in- 

 terposed ; some of the white and caerulean varieties are hydro- 

 phanous; others have a very delicate coating of aluminous 

 matter, which causes their colour to deepen considerably on 

 the application of moisture. Pseudo-morphous crystals of this 

 substance also occur, formed within cavities from which other 

 crystallized substances have been by some natural cause, (pro- 

 bably solution,) removed. Irregular masses of siliceous mat- 

 ter that have obviously invested, either wholly or partially, cry- 

 stals of iron-ore. Iron-pyrites, quartz or garnet, are of frequent 

 occurrence. I have specimens of the substance in moulds of 

 this kind, and conceive that much of (if not all) the Haytorite 

 (as those crystals have been named) is referable to some of the 

 different forms of the above substances, and is chalcedonic 

 matter filling the said cavities by stalagmitic deposition ; some 

 of the faces of the crystals are very splendent, others rough ; 

 in some of the crystals all are rough : the fracture is different 

 from that of a true crystal, nor have I ever succeeded in ob- 

 taining a regular cleavage ; the crystals are of various sizes ; 



3 A 2 the 



