Page:Quarterly Journal of the Geological Society of London, vol. 26.djvu/293

 tertiary times — and cannot doubt, from the physical condition of the vales of the Severn, Gloucester, and Berkeley, &c, that the finely exposed western escarpments of Oolite, and still more eastward ranges of Cretaceous rocks, in fact the whole Secondary series, once covered and arched over the now deeply exposed and denuded Lower Mesozoic and Palaeozoic rocks that constitute the mass of the country west of the Cotteswold range. What influence and changes these valleys underwent still later, or during the Pliocene and Post- pliocene epochs, I would leave to be discussed in a special paper upon the age of the Severn valley.

I believe, then, that it was during the progress of the denudation of the palaeozoic rocks by the seas of the Triassic epoch that the pre-existing faults and fissures, or open joints, &c, along the coast-lines, were mechanically and chemically filled in. The colour and nature of the New Bed marls and sandstones, fully attest the presence and abundance of the peroxide and protoxide of iron at the time of their deposition, due perhaps originally to the oxidation of the materials contained in the older carboniferous rocks, which became thus metamorphosed during removal and deposition. The chemical condition of the saline waters, or even water at a higher temperature than that of the modern seas of Europe, may have tended to the more rapid deposition or accumulation of the iron &c. in the faults and fissures.

There are many localities in and around the Bristol coal-field where full and complete evidence can be obtained as to the age of the infilling of these dislocations &c. in the Carboniferous Limestone, Millstone Grit, and Pennant, due to the destruction of the older rocks by that sea which also deposited the conglomerate and associated New Bed series.

At Broadfield Down, south of Bristol, Providence Place, near Ashton, many places on the Mendip Hills, as well as north-west of Bristol, along the west side of the coal-basin, where the hydrous oxides of iron are worked, the broad and exposed surfaces of the limestone and grits are planed away and laid bare ; and here and there in the depressions pockets occur, the remains, or remnants, of the earliest- formed portion of the dolomitic conglomerate. So also with the fissures and faults which are usually filled with the magnesian breccia, the cementing matrix in many cases being the brown and red hydrated peroxides of iron as well as the dolomites, the qualities and quantities of the ore differing with the matrix or rock in which it occurs. Doubtless the percolation of water through porous overlying strata highly charged with the oxides of iron, as is the case with the New Red series, has also been a source and mode of accumulation ; and this phenomenon or mode of production is now in operation along the lines and in and upon the walls of the great Ram Hill and associated fault that traverses the northern coal-basin, as, notably, at Brampton Cotterell.

It is, however, to Clifton that my paper has chief reference, as I am desirous of fixing the exact position of the locality where the remains of Thecodontosaurus and Paloeosaurus were discovered by

o 2