be realized by any but those who have devoted themselves to the study of practical geology. Thus, we know that from the top of Skiddaw there has been removed no less a thickness than 30,000 feet of solid rock! From the Western Highlands of Scotland, as well as from the surface of many Cornish moors, strata from 30,000 to 50,000 feet thick have been weathered away. It is certain that all the now-exposed Laurentian and Cambrian rocks of the north-west of Scotland were once buried beneath thousands of feet of Silurian rocks. These have since been eaten away, and the Cambrian and Laurentian rocks laid bare. The latter are the oldest in the geological record, and such grand and abrupt mountains as Suilven in Sutherland are entirely composed of Laurentian rocks, surrounded by a framework of hills formed of Cambrian strata, which latter have been denuded from and about old Suilven. The hills and mountains of Cumberland and Wales are of later date, but they have hardly suffered less from denudation. They are lower in height now than ever they were before in the geological history of our planet, for their ridges and summits have been continually weathered since they were first upheaved above the general level of the earth's crust. Most of our oldest hills are formed of Cambrian and Silurian rocks. Nearly all those of Scotland are, with the exception of the rugged mountains of Sutherland. The Highlands, the Pentland and Lammermuir hills, the Grampians, the Cumberland mountains, those of Shropshire, North Wales, of Connemara, and elsewhere are distinguished by

the large proportions of rocks of this particular age which enter into their composition. The softer strata of the later Old Red Sandstone period have been more eaten away, so that we never have rocks of this age forming high mountains, although they often compose undulating hills, such as those of Herefordshire and the sides of the Mendips. In Devonshire the harder slates, formed later still, give rise to bolder scenic features, as in the Quantock hills and the neighbourhood of Dartmoor.

We next come, in the order of geological succession, to such of our British hills and mountains as are formed of Carboniferous rocks. Mountains they seldom or never rise unto, for we rarely have elevations formed by rocks of this age of more than 2,000 feet above the sea-level. They form hilly and moorland scenery rather than mountains. The grandest scenery produced among Carboniferous rocks lies where the lower subdivision of limestone comes up. Owing to its great hardness it enters into the structure of some of our highest and most extensive English hills, and in the earlier history of geology it went by the name of "Mountain Limestone" for this very reason. The finest hills formed of this rock are those of the Peak of Derbyshire. Penyghent, Ingleborough Fell, the Eglewysg Rocks at Llangollen, are other well-known hilly districts where this formation occurs. The Millstone Grit composes much of the hilly regions of Yorkshire, Lancashire, and Derbyshire, forming the Pennine chain; Kinder Scout, in the latter county, being almost entirely composed of this rock. Then we come

to the strata of Permian and Triassic age, usually soft and easily weathered, and therefore forming the dales and plains of Cheshire, Worcestershire, and elsewhere. Although occasionally we have some member of the harder subdivisions rising into hills, as, for instance, Alderley Edge, and Beeston Hill, crowned by its grand old castle, in Cheshire. The Oolitic rocks, which extend in a belt across England, from the Yorkshire to the Dorsetshire coasts, frequently form hills and exhibit steep escarpments. The Cleveland Hills and Cotteswold Hills are composed of these rocks. The Chalk, in Yorkshire, Lincolnshire, Sussex, and Kent, rises into those rounded hills termed "Wolds" and "Downs," which have a scenery peculiarly their own.

Thus, it will be seen that our British mountains and hills are formed of rocks of different geological ages, and that both the hills and the materials composing them have their origins referred to various geological epochs. It is believed that the Wrekin, in Shropshire, is the oldest mountain in England, if not one of the oldest in the world. Its main mass is composed of volcanic materials, bedded and stratified, which were ejected from a crater not far distant from the present site of the mountain, during a geological period long before the Cambrian. The base of the Cambrian rocks in the neighbourhood is formed of a conglomerate of pebbles actually derived from part of the most ancient mass of the Wrekin. Deposition has since then buried it beneath thousands of feet of rocks of later date, and denudation, chiefly carried on during the Tertiary period, has stripped them off again.

Many of our British mountains owe large portions of their masses to volcanic agency; although we cannot say that many of them are ancient volcanoes. The highest mountain in the Isle of Mull is above 3,000 feet high; and Professor Judd has demonstrated that it is the boss or denuded base of a volcano which was in active operation during such a geologically recent period as the Miocene. When in the zenith of its energy Professor Judd is of opinion it must have been from 12 to 15 thousand feet in height. The bosses of several ancient volcanoes in Cumberland have been described by the Rev. J. Clifton Ward, some of them, as Castle Head, forming notable scenic features about Lake Derwentwater. Among those of our British hilly regions indebted to volcanic agency for the whole or part of their rock-masses may be mentioned the following:-The Cheviot range; the mountains and hills in and about Kirkstone Pass, in Cumberland, where there is abundance of green volcanic ashes and volcanic breccias, in places 6,000 feet in thickness. The neighbourhood of Snowdon (especially at Llanberis), of Dartmoor, the Wrekin, the hills of Charnwood Forest, the Cornish hills, Mount Sorrel, in Leicestershire; Rannock Moor, up to which the famous Pass of Glencoe leads, in the Western Highlands of Scotland, &c. These volcanic results spread over many periods of geological time; although there can be no question that the Silurian was an epoch when volcanic activity was especially great in what is now the British islands. Many thousands of feet in thickness of rocky matter were then disgorged, and turned inside out of the earth