formed first and the second set by a separate and subsequent movement, but it is certain that the interference or combination of these axes has produced the broad basins in which the Coal-measures are now found. The system of east and west flexures is particularly well marked in Ireland, the pre-Dyassic movements acting most forcibly over the northern and southern districts, and raising the whole central mass of country between them. In the south of England there is a set of ridges similar to those in the south of Ireland, passing from Devon and Somerset beneath the newer rocks of the southern counties into Belgium and the north of France. It is also very likely that the tract of Palæozoic rocks which underlies the east of England was elevated at this epoch. Simultaneously with these upheavals it is very probable that the ancient Atlantic continent was broken up, submerged, and converted into an open ocean; the depression of this Atlantic area being in fact the proximate cause of the upheavals on either side. Such, according to Professor Hull, was the genesis of the North Atlantic Ocean,1 and, apparently, it has never ceased to be an ocean from that time to the present day, though throughout the Mesozoic periods there was a large continuous tract of land to the west of England, of which Ireland, Wales, and Cornwall are now the sole remnants. It may, in fact, be said that the rock-masses out of which Ireland, Scotland, and the greater part of England have been hewn, were now, for the first time, brought into connection as a compact mass of land. The greater part of this land region lay to the south and west, spreading from the north of France, through the south of England, to Wales and Ireland, and thence, by way of the Hebrides, to Scotland and the Border counties. It was not Britain, 1 "Physical History of the British Isles," 1882, p. 44. but a West-European continent, which presented a continuous front to the Atlantic, considerably to the west of what are now the shores of France and Ireland. It is now time to seek for the boundaries of the seas and lakes in which the Dyassic sediments were deposited. The open Mediterranean sea of the Carboniferous period appears to have been converted into a large inland sea, like the Caspian of the present day, surrounded by a rocky and hilly continent, on which grew trees and plants of various kinds. Many of these plants are closely allied to those of the Carboniferous, but species belonging to the Yew and Fir tribes, which flourish on dry ground, preponderate over the reeds, ferns, and gigantic lycopodia which flourished in the Coal-measure swamps. The western part of this inland sea stretched across the centre of what is now the North Sea, and covered a portion of north-eastern England, and its actual margin seems to have lain only a little to the west of the outcrop which now runs through the counties of York and Nottingham, curving round to the eastward beneath the south of Lincolnshire. If the Pennine range formed a continuous barrier in Dyassic times, its eastern slope must naturally have been the shore-line of the Magnesian Limestone sea, and such is now the prevalent opinion; but it is only fair to state that the geologist who first studied the uplifts of the Pennine range1 came to the conclusion that they were postDyassic. Strong arguments were, however, subsequently adduced by other writers to show that he was mistaken, and it is perhaps desirable that the reasons for the view here adopted should be stated seriatim.2 1. The flexures of the South Yorkshire and Derby coalfields are certainly pre-Dyassic, and as their major axes 1 Hull, in "Quart. Journ. Geol. Soc.," vol. xxv. p. 171. 2 See Wilson, "Geol. Mag.," ser. 2, vol. vi. p. 500, and Teall, vol. vii. p. 349. are parallel to the central Pennine axis, we may safely assume that they were both formed at the same time. 2. After crossing the Millstone Grit area of central Yorkshire, the outcrop of the Dyas again passes on to Coal-measures in the south of Durham, showing that all the flexures between the two coal-basins were preDyassic. 3. No Dyassic outliers occur at any distance west of the main escarpment, and no fragments of Magnesian Limestone have been found in the Triassic rocks, as might have been expected if that limestone had passed over the Pennine axis, and had been subjected to erosion in Triassic times. 4. On the other hand, fragments of Carboniferous Limestone are said to have been found both in the Dyassic breccias and in the Triassic sandstones, which would prove that this limestone had already been bared along the Pennine axis. 5. The Dyassic rocks on opposite sides of the Pennine range are very dissimilar, the thin local beds of magnesian limestone on the western side bearing no comparison with the massive dolomites of the eastern tract, while the red sandstones are essentially a feature of the western districts. It might perhaps be doubted whether the range formed a complete barrier, and whether there was not communication between the two areas of deposition by means of a narrow strait across the centre of Yorkshire. The only piece of evidence in favour of such a communication is the occurrence of Magnesian Limestone fossils in the limestones of Lancashire and Ireland, but as both the eastern and western areas were uplifted portions of the Carboniferous sea, the same forms of life are likely to have remained in both, even if one was rapidly isolated by the upheaval of a barrier. On the whole, therefore, the |