The contents of this paper record the results of a detailed examination of certain extensive areas of dolomitization in the Carboniferous Limestone of the Midlands. During the period 1912 to 1914 the faunal succession in the Carboniferous Limestone bordering the Leicestershire Coalfield chiefly claimed my attention, but many problems associated with dolomitization arose in connexion with that work and have been discussed in a previous paper. Being thus introduced to a study of metasomatism which yielded interesting results in Leicestershire, I turned my attention to the larger Carboniferous Limestone outcrop in Central Derbyshire, where a considerable thickness of dolomitized beds awaited description. The question as to whether the dolomitization in Derbyshire affected material on similar horizons or exhibited other features analogous to those of the dolomitization of the Leicestershire outcrops afforded considerable scope for investigation. Additional incentive to this particular study lay in the fact that dolomitization in the Carboniferous Limestone of this country had not been treated as a principal theme, but had been briefly described in notes occurring in papers by various authors, whose main object was the elucidation of other problems such as faunal succession.

An excellent exposure of a Raised Beach has lately been discovered at Easington. This deposit, in my opinion, forms a part of the beds of sand, gravel, conglomerate, and breccia which are exposed along this part of the Durham coast for at least 5 or 6 miles, and which were described by me as Raised Beaches in 1905. I also consider that the upraised littoral formations were produced in late Pleistocene times.

The area under consideration extends from the mining town ot Egremont to Scalesmoor Farm in the parish of Lamplugh in West Cumberland, and comprises a tract of country 9 miles in length and rather less than 3 miles in width, running from S.S.W. to N.N.E. It forms the south-eastern margin of the Whitehaven Coalfield, and is the western portion of the “collar” of Lower Carboniferous rocks almost surrounding the older Palæozoic rocks of which the Lake District proper is composed. The area consists in the main of fahly continuous outcrops, but is much disturbed by faulting. In the unravelling of the tectonics of the district, however, the difficulty caused by excessive faulting is counterbalanced by the multiplicity of the borings that have been made during the exploration and development of the valuable haematite deposits associated with the limestones. In no single instance is there an exposure giving a complete section of the sequence, yet with the help of the journals of the “bores” every one of the exposures mentioned in this paper can be placed at its exact horizon with great accuracy.

The occurrence of iron carbonate as a part of the cement in the Pennant Sandstone is not extraordinary, when the large amount of entombed organic matter is taken into consideration. The presence of organic material and the products of decay, the so-called humus acids, acting as reducing agents, would aid in the formation of iron carbonate and prevent its oxidation. Much of this carbonate probably owes its presence to a metasomatic replacement of calcium carbonate. The granules of siderite may have been derived from rocks similar to those of the Lower Coal Series of South "Wales. The alkaline carbonates which hold the humic substances in solution would readily dissolve silica, thus becoming effective agents in the solution and redeposition of silica in the rock. A solvent of this kind would be formed by the impregnation of alkaline salts by carbonic acid.1 The occurrence of so much secondary silica in the rock is probably the result of a redeposition of silica from such a solution. No oxides of iron have been found in any of the numerous separations, either by means of heavy liquids or the electro-magnet; their absence is easily explained when we consider the strongly reducing environment of the deposition and consolidation of the Pennant Sandstone. The perfectly rounded globules of sphserosiderite may have been precipitated whilst the sandstones were being deposited, but more probably derived from the denudation of fireclays similar to those of the Lower Coal Series of South Wales.2 The dominant mineral chlorite, existing as perfect cleavage flakes, is entirely distinct from the secondary aggregates of chlorite in the rock, and was probably deposited in its present form. I have examined a powdered specimen of the Delabole Slates of Cornwall (Upper Devonian), and have found in it a large proportion of chlorite flakes, exactly like the detrital chlorite of the Pennant Sandstone. The very few flakes of biotite found show little trace of alteration. The paucity of heavy minerals indicates that the Pennant sediments had not a granitic source; they were mainly derived from pre-existing sediments which were rich in chert, had abundant chloritic material present, and yet were capable of furnishing fairly fresh biotite. Metamorphosed shales would account for the presence of cordierite and corundum.