Page:Transactions of the Geological Society, 1st series, vol. 4.djvu/28

 abundantly impregnated with yellow ochre, which is sold under the name of die-sand.

Fire-stone resembles the grindstone in colour and fracture, but is soft when first worked. The best is quarried at Burradon near Killingworth: glass-house furnaces are constructed with it.

White post is a fine-grained sandstone, tolerably hard.

White post with whin consists of alternate laminæ of soft and hard sandstone.

Grey post is a fine grained sandstone, containing a large admixture of clay and sometimes of mica.

Brown post is a slaty micaceous sandstone.

Brown post with Coal pipes is a laminated sandstone traversed by strings of black shale and coal.

Brown post with skamy partings is a light brown sandstone with dark brown lamina.

Grey whin or Brown whin is a very hard dirty-brown quartzose sandstone, sometimes specked with minute white dots, and at other times containing very small scales of mica: it strongly resembles granular quartz. A bed of this rock may be seen contiguous to the basaltic dyke in Walbottle Dean.

What is called by the miners Band in coal is commonly composed of bituminous shale, clay and iron pyrites; sometimes of sandstone. Girdle means a thin plate: thus Post girdles are layers of sandstone; Whin girdles in post are layers of hard quartzose sandstone in softer sandstone; and Whin girdles in shale are thin beds of argillaceous iron ore in shale.

The minerals that accompany the coal measures are,

Clay ironstone, forming either thin beds or nodules (catheads) in the shale.