Page:Transactions of the Geological Society, 1st series, vol. 4.djvu/216

 magnesian limestone lies over the coal measures; it is doubtful however whether the coal measures are conformable with the strata of the magnesian limestone; and it is not improbable that they lie under it, having the edges of their tilted and broken sills abutting against the lower surface of the superincumbent rock.

The red marl is so widely distributed in that part of England which lies between Lancashire and the southern coast of Devonshire, and is so frequently found in that district in the same geological position which it occupies in the northern and midland counties in alliance with the magnesian limestone (lying for instance in horizontal strata upon the inclined coal measures, and bounding them at their basset) that it might be expected in some part of its course to discover traces of the magnesian rock. Accordingly I shall mention some instances of the occurrence of a magnesian limestone in the district above referred to, where it either alternates with red marl, or may be considered as connected with it.

In the course of a valuable paper on the Rocks in the vicinity of Bristol, which was long ago presented to this Society, the author, Mr. Bright, has given an account of the strata of red marl which lie along the banks of the Avon. The red marl is there found either lying upon the coal measures, or filling up the vallies that are occasioned by the breaking off of the inclined strata of limestone, where instead of the series of inclined strata that should rise from beneath the limestone, horizontal strata of red marl are found resting upon the broken edges of the limestone or of the first of the rocks beneath it. It is in the red marl last described, as it occurs near Hung-road on the Avon, that Mr. Bright discovered a limestone breccia, of which there are two beds alternating with red marl.

Having examined this breccia on the spot, after having consulted Mr. Bright's paper, and having seen some breccias from the Mendip