On the Junction of the Silurian Rocks and Carboniferous Limestone On

Downloaded from http://pygs.lyellcollection.org/ by guest on September 30, 2021 309 JUNCTION OF THE SILURIAN HOCKS WITH THE OVERLYING MOUNTAIN LIMESTONE, AT MOUGHTON FELL, IN RIBBL1S- DALE. BY THE EDITOR. (SEE PHOTOGRAPH.) THE photograph issued with this year's volume of proceedings, illustrates an important section exposed in the valley of the Bibble, nearly opposite the village of Horton. The Silurian rocks, composed of grits, slates and limestones, extend over a large area, bounded by the line of the Pennine Fault, running in a north and south direction, and that of the equally important series of Craven Faults which run eastward from Ingleton, their position being indicated by the precipitous Scars of GiggXeswick, Attermire, Malham, Yordale and Kilnsey. Bounded on the west and south by these Faults, the Silurian rocks underlie all the highest moun• tains in Yorkshire, forming a tolerably even base, with a general dip to the north-east. Sections exposing the junction of these rocks with the superincumbent Mountain Limestone may be seen beneath Whernside and Ingleborough, in the Ingleton and Dale Becks, and in Clapdale; underlying Cross Fell and Mickle Fell, they may be seen at High Cup Gill, and as shown by Mr. Dakyns, at the Pencil Mill, near Cronkley Scar. Penyghent, and the extensive Limestone Fells of Malham and Kilnsey also have a basement of Silurian Grits. Perhaps the finest section, showing the junction of the two formations, anywhere exposed, is the one chosen for the subject of this photograph. The Silurian Rocks have long been quarried, and are locally known as the Horton Flagstones; they are a bluish grey colour, rather coarse structure, and can be obtained of very large size. The flags are inclined at a very sharp angle to the horizontal beds of limestone which lie above them, but if traced along the side of the hill, it will be observed that they do not dip uniformly Downloaded from http://pygs.lyellcollection.org/ by guest on September 30, 2021 310 in the same direction, but are doubled into a series of anti- clinals. It appears probable, that after the deposition of the bed of sand and mud forming these rocks in the ancient Silurian Sea, they were elevated and subjected to violent lateral pressure, and after this, that there was a long period when the rocks so formed were again beneath the waves, and were ground down by attrition to their present nearly level surface. On this, the coral reefs and shell beds forming the great mass of the Mountain Limestone was gradually accumulated. In many instances, there is between the two series of strata, a layer of pebbles derived from the Silurian Rocks beneath, and rounded by the action of water until all the sharp edges are worn off. Such a mass of pebbly conglomerate may be observed in the section photographed at the point where the water is thrown out, forming a pretty cascade. This conglomerate has been described as a detached mass of Old Red Sandstone, but the probability is that it must be considered as a part of the Carboniferous Limestone series, constituting a good dividing line between these and the Silurians, or as a basement bed to the Limestone. MINUTES AND BALANCE SHEET. Meeting of Council at the Philosophical Hall, Leeds, on February 28th, 1877. Prof. A. H. GEEEN, M.A., in the chair. Present—Prof. A. H. Green, Messrs. Davis, Brigg, and Embleton. The Secretary read the minutes of last meeting, which were confirmed. The Treasurer read his report; moved by Mr. Davis, seconded by Mr. Embleton, and carried—" That it be adopted." .

Load more