probable, therefore, that they are concealed under the other beds there by means of such a downcast fault. Several other faults have been found affecting the margin of the red marls, as may be seen in the map.
We have already mentioned a south-west and north-east fault, supposed to start from the sides of the quartz ridge near the coalmeasures, and run to the north-east. This has a downthrow to the south-east, and brings down the New red sandstone level with the ends of the Silurian. Coal-measures and Permain beds, between the Colmers and Mason's Lodge. Farther to the north-east it brings the red marl down against the lower part of the New red, namely, the brick-red sandstone, and it then runs off to the north-east through Birmingham, up nearly to Sutton Coldfield, bringing the red marls down against various parts of the New red sandstone. From the eastward of Sutton Coldfield the red marls stretch to the northward uninterruptedly to those before mentioned, north of the Trent, between Barton-under-Needwood and Abbott's Bromley.
The New red sandstone included between this marl boundary and the coal-field consists of brick-red sandstones near Birmingham, part of the upper Bunter sandstone, lying either horizontally, or dipping very slightly to the east, and allowing of the outcrop of a thickish band of pebble beds that usually form the boundary of the New red towards the Permian district. These pebble beds may be traced, more or less continuously, from the Lightwoods near Harborne to Barr Beacon. They apparently extend eastward a good way about Sutton Park, but they approach the boundary of the coal-field again about the Brown Hills, and coming against the fault are cut off by it, dipping north under the upper part of the New red, and only just rising up and re-appearing at the surface on the high ground west of Brereton, from which place they join on to those of the north part of Cannock Chase. Between Lichfield and Rugeley we have only the upper parts of the red sandstone, those lying just below the red marls as before described; so that if the ground were a little higher, the tops of the hills would all be capped by the red marl, as is the hill at the Old Lodge.
CHAPTER XIII.
On Faults.
The previous Chapters have been confined almost entirely to the description of facts actually observed. In the present Chapter it is intended to make some remarks on the proper use of the term "fault," and on some facts tending to throw light on the origin of faults and their mode of production.
The word "fault" is one of several that have been selected by geologists from the language of practical miners, and adopted as scientific terms. Various synonyms for it are used in different
