These very thick seams are, however, rarely constant in character for any great distance, being found commonly to degenerate into carbonaceous shales, or to split up into thinner beds by the intercalation of shale bands or partings.
The nature and extent of these operations vary with the character of the coal, which if hard and free from shale partings may be finished by simple screening into large and nut sizes and smaller slack or duff, with a final hand-picking to remove shale and dust from the larger sizes.
C. Marsh, by finding the imperfect fossilized tibia of a bird in the middle cretaceous shale of Kansas, Marsh, began a series of wonderful discoveries of great im portance to ornithology.
The district is rich in limestone, coal, ironstone, shale and fireclay, all of which are worked.
Occasional beds of tuff are intercalated among these lavas, and likewise seams of fine clay or shale which have preserved the remains of numerous land-plants.
In England, Kimmeridge Clay, Lias clays, London Clay and pulverized shale and slate are all employed for this purpose.
Thick, with beds of calcium phosphate, and a shale of half that thickness, were discovered by Hope Jones in the neighbourhood of Cwmgynen, about 16 m.
The surrounding country is a magnificent livestock and farming region, and in the immediate vicinity are valuable deposits of coal, of limestone, of shale suitable for sewer pipe and of fire clays.
Laterite, shale and sandstone occur all over the district.
Kerosene shale (torbanite) is found in several parts of New South Wales.