Page:Transactions of the Geological Society, 1st series, vol. 1.djvu/211

 sixteen feet at Old-park, and eighteen feet at Ketley. That the Viger coal, with its superincumbent clay, occupies thickness of about twelve feet at Madeley, is diminished to three feet at Lightmoor, and is entirely wanting in all the collieries which lie to the north of the latter. That a bed of clay, usually known by the name of the upper clunches, bears a thickness of from fifteen to twenty-six feet in all the above mentioned collieries, except that of Ketley, where it is entirely wanting.

The rock upon which the coal formation rests, is either die-earth or limestone.

The die-earth, or dead earth as it is also called, is a name given by the miners to this bed as indicative of the fact that from hence downwards all the coal strata die or cease. Its colour is greyish; and it consists of fine sand, of particles of limestone, and of clay, mixed together in very various proportions; it is often also micaceous. It has sometimes a strong tendency to a slaty structure and a stratified arrangement, with which also the direction of the spangles of mica that it contains for the most part corresponds. It contains a few bivalves, chiefly of the genus cardium, and the entomolithus paradox us, or Dudley fossil. The thickness of this bed is very various, from a few feet to an hundred yards; it incloses fragments of limestone, and is interposed between the limestone and the coal-formation without possessing the dip or direction of either one or the other.

In order to obtain a clear idea of the limstone-formation, it will be necessary to commence our observations at the south-eastern extremity of the district here described, where we shall find two parallel ranges of limestone running nearly N.E. and S.W. Of these ranges, that which lies the most easterly will first engage our attention.