We may conclude this chapter by saying what we imagine of the general appearance of our own islands to have been. At the close of the Silurian period Britain was probably an archipelago, ranging over ten degrees of latitude, like many of the island groups now found in the great Pacific Ocean; the old gneissic hills of the western coast of Scotland, culminating in the granite range of Ben Nevis, and stretching to the Southern Grampians, forming the nucleus of one island group; the South Highlands of Scotland, ranging from the Lammermuir Hills, another; the Pennine chain and the Malvern Hills, the third and most easterly group; the Shropshire and Welsh mountains, a fourth; and Devon and Cornwall stretching far to the south and west. Every spot of the island lying now at a lower elevation than 800 feet above the sea was under water at the close of the Silurian period, except in those instances where depression by subsidence has since occurred. CHAPTER XVIII HOW THE COAL BEDS WERE LAID DOWN In following the history of the rocks, we shall have presently to speak of that period which embraces the strata which contain coal. The geologists who lived in the early part of last century--William Smith and others--noticed that beneath the coal-bearing strata there lay a considerable thickness of red sandy beds containing the remains of fresh-water fishes, shells, and plants, while above the coaly strata they found another thick mass of red sandstone. To the lower and older red rocks they consequently gave the name of Old Red Sandstone, and to the upper and newer ones the name of the New Red Sandstone. The Old Red Sandstone formation, therefore, lies between the Silurian rocks below and the rocks of the coal period above. But in Devonshire we find a considerable thickness of shales, slates, and limestones containing _marine_ fossils, and these also lie between these two formations, and must therefore be somewhere about the same period, or geological age, as the Old Red Sandstone. The name "Devonian" has therefore been given to these shales, slates, and limestones, which were evidently being deposited in an open sea at or about the same time at which the Old Red Sandstone strata were being laid down on the floors of inland fresh-water lakes.