ABSTRACT
The coal in Great Britain was formed many millions of years ago by the action of heat and pressure on decayed vegetation. Giant fern-like trees grew in and near swampy lakes and, as they de¬cayed, formed deposits of vegetable matter. Changes in the surface of the earth resulted in these deposits being covered by layers of sand and mud and succeeded by further layers of vegetation and sediment. Later these layers became buried under hundreds or even thousands of feet of rock, and the heat and enormous pressure of the rock changed the vegetable matter into coal. The muddy sediments became the shale and other dirt now found with the coal. Earth movements resulted in the layers, or strata, of rock and coal being bent and folded, so that sometimes the coal outcrops to the surface, and at other times lies thousands of feet below. The strata may have been fractured by these move¬ments, resulting in faults as shown in Fig. 1. The coal occurs in bands from a few inches to several feet in thickness and varies considerably in chemical composition and quality. The distribution of the coalfields is shown on the frontispiece map.
