GENERAL VIEWS. 179 
Teesdale and Aldstone moor, for beds of the Yoredale series. The 
main limestone is bluish in that district, but grows gray or even 
whitish toward the south-east. The lowest beds of Brough are smoky, 
yellowish, and mottled. 
Specific Gravity. — Limestone lying on the grauwacke of Mougliton 
fell, (hard, compact, and black,) 2-785; ‘Dun lime’, granular, and 
crystalline; Mougliton fell 2-81; Kettlewell 2*79; Ingleton 2 '77 ; 
Kirby Lonsdale (bed) 2.744 ; Biggin near Kirby Lonsdale 2’735. Lime- 
stone lying on the Whin sill, white and crystalline, 2’68 ; compact 
limestone of Kirby Lonsdale, Casterton, and Barbon, 2-70 ; red lime- 
stone of Kirby Stephen 2-597, 2-608 ; yellowish beds of Ash fell 2'60 ; 
sonorous limestone of Biggin 2-70. Main limestone of Ingleborough 
2-66; Hardrow scar limestone 2*73 ; black argillaceous limestone of 
Pendle hill 2'69. Nearly all the dark varieties yield the disagreeable 
smell of swinestone on being struck or powdered. 
Chert. Composed of silica, with uncertain admixtures of calcareous 
and argillaceous earths: texture compact, with splintery and hackly 
fractures, finely granular, or laminated: colour white; gray tinged 
reddish, yellowish, bluish ; black ; mottled and shaded. Specific gravity 
2-3 to 2-5. Forms beds above the main and underset limestone, in 
Swaledale, Wensleydale, and Bishopdale ; nodules in the main lime- 
stone and underset limestone of Coverdale, &c. ; narrow bands and 
nodules in the black limestones of Craven. It bears in these cases the 
same relation to limestone as flint to chalk. The light-coloured sorts 
are liable to decomposition, and then yield white or brownish powders, 
and organic remains. The chert rocks above main limestone are usually 
very much fissured, so as to fall to fragments on being shaken. Some 
varieties pass to plate, others to gritstone, others to limestone. 
Plate may be viewed as a series of interrupted deposits of bitu- 
minous clay, condensed and indurated into a finely and regularly 
laminated rock. There is usually some oxide of iron in the mass ; 
its colour almost uniformly black or dark gray; slightly micaceous, 
A a 2 
