On the Red Beds at the Base of the Carboniferous Limestone in the N.W. of England

Abstract

Between the silurian and the carboniferous systems there occurs a great thickness of red and yellow sandstones and conglomerates, to which the name of old red sandstone has been given. These beds appear to have been deposited in shallow, brackish, or fresh waters, caused by the gradual shallowing and contracting of the silurian sea. The fossils of the upper silurian beds become fewer in number and dwarfed in form as they pass upwards and finally disappear, and all traces of marine shells die out, while land plants and fresh water fishes become the characteristic forms. The old red sandstone of Shropshire, Hereford, and Wales lies regularly and conformably upon the upper Ludlow rocks, and after attaining a thickness of 10,000 feet, passes upwards conformably and without any break into the carboniferous limestone. In Scotland there are two old red districts, one south, and the other north, of the Grampians. The beds of the southern region are divided into three groups. The lower lies conformably upon the upper silurian, the middle lies unconformably upon the lower, while the upper lies unconformably upon the middle, but passes upwards conformably into the carboniferous rocks. In the northern region, also three divisions are recognisable, but there is no unconformability between them. The lower rests unconformably upon lower silurian rocks, and the carboniferous rocks are absent. In the South of Ireland, the beds which intervene between the silurian and carboniferous systems are naturally divided into two sets; the Dingle beds, consisting of coloured grits, slates ...