By the continued elevation of the Silurian sea-floor, large portions became dry land, and during the succeeding period most of the British area formed part of a continental mass. Over the southern part of England, there still lay an arm of the sea, and in this were laid down the marine sediments which now form part of Devon, and from which the name Devonian has been taken as a convenient designation for the strata of this period. In parts of the northern land, in the region now occupied by Scotland, there were large inland lakes, on the floor of which vast thicknesses of shingle beds and coarse sands (“Old Red Sandstone”) were slowly accumulated; and it has been shown by Sir Archibald Geikie and others that during this epoch there were considerable outpourings of volcanic material in the Scotch area. Farther to the West and South-west there was another large lake in which the so-called Kiltorkan beds of Ireland were deposited. In these Irish sediments, and others of the same age in Belgium and elsewhere a few forms of land plants have been discovered; but it is from the Devonian rocks of North America that most of our knowledge of the flora of this period has been obtained. VI. =Carboniferous.= From the point of view of palaeobotany, the shales, sandstones, and seams of coal included in the Carboniferous system are of special interest. It is from the relics of this Palaeozoic vegetation that the most important botanical lessons have been learnt. The following classification of Carboniferous rocks shows the order of succession of the various beds, and the nature of the rocks which were formed at this stage in the Earth’s history. ╭ Upper Coal-Measures. ╭ Coal-Measures[53] ┤ Transition Series. │ │ Middle Coal-Measures. │ ╰ Lower Coal-Measures. │ Millstone Grit. CARBONIFEROUS ┤ ╭ Upper limestone shales │ │ and Yoredale rocks. │ Carboniferous limestone ┤ Carboniferous or │ series │ Mountain limestone. │ ╰ Lower limestone shales. ╰ Basement conglomerate. In the classification of Carboniferous rocks adopted in Geikie’s text-book of Geology the following arrangement is followed for the Carboniferous limestone series[54]:—