MINERALOGY OF ARRArf. 



347 



Within tide are several strata that look like a Mosaic Naturd Mosaic 

 pavement of finely polished brick, of a florid red colour. p 

 They consist of equilateral pieces, or rhombi, of indu- 

 rated clay, divided by septaria which run in straight lines 

 parallel to each other, and are crossed by other straight 

 And parallel lines with the greatest regularity, so that each 

 rhombus is enclosed within septaria, which separate its 

 sides from those of other rhombi, which are parallel to 

 them. The breadth of the rhombi may be about fourteen 

 inches; that of the septaria about half an inch. The 

 colour of the septaria is a pale red, inclining to whiteness; 

 and it looks very like puzzolana cement, in the interstices 

 between regularly formed stones. In many cases the pave- 

 ment is worn down ; but the cement, which is harder, pre- 

 serves a regular equality of height. 



I doubt much if the most skilful mason, or even a ma- 

 thematician, could produce any thing more regular, or 

 more beautiful. 



Here are numerous strata of red clay shiver, and of red Iron or«. 

 slaty schistus, which include various stratulae of haematites, 

 and of kidney ironstone. The haematites is generally ar- 

 ranged in stratulae, but often interspersed. When stratified, 

 it generally comes off in rounded pieces, whose sides are 

 perpendicular, and are thicker towards the Centre, thau 

 towards the circumference. When interspersed, the pieces 

 are generally broader, are of a round, or oval form, and 

 fattened towards the circumference. 



The pieces that have been long exposed to the air are of 

 a blood-red colour, though darker towards the centre. 

 Uut by a* little digging, pieces are found, with a red teg- 

 men, but internally of a fibrous texture, the fibres at right 

 angles to the breadth of the stone, and the colour that of 

 steel. The interspersed pieces often exhibit an indented 

 fracture, where the surface of indentations has the lustre 

 of steel. 



The kidney- form pieces often exhibit a dull red earthy 

 appearance to their centre. But, where they have not 

 been too much exposed to the atmosphere, they discover a 

 radiated texture, with the lustre of steek 



These two species feel very heavy; but there are also 

 2 A 2 other 



