4. Gradual submergence of the land to a depth in Wales of not less than 1,400 feet. Depression probably partial and dying out rapidly towards the south. Climate temperate, but passing to cold-temperate, and to arctic in Scotland.

5. Gradual re-elevation of the land. Snowfields and glaciers increase until for the last time all Scotland, Wales, and the northern districts of England are covered with an ice-sheet.

6. Retreat of the ice. Great floods from the melting ice distribute vast quantities of gravel and sand over the low grounds.

7. Period of great local glaciers. Land of less extent than now. Floating ice. Climate arctic.

8. Britain becomes continental. Summer and winter temperatures more excessive than now. Age of great forests. 9. Final insulation of Britain. Climate humid. Decay of the forests and accumulation of peat-mosses. Land of less extent than now. 10. Partial re-elevation; climate temperate; the Present.1

This summary will be sufficient to indicate the great changes that have taken place since Pliocene times, changes which have not only modified the life-history of different tracts, but likewise the character of the sediments, rendering the minute examination of the various superficial deposits a matter of the greatest interest. And yet as they are more minutely divided in different localities, we find a greater difficulty in classifying them according to time, than is experienced in the larger divisions of the older stratified rocks.

Glacial Deposits.

The Glacial deposits, or rather the deposits of Glacial age, include various gravels, sands, loams, and clays. The term 'Boulder Clay' is applied essentially to the deposits of a clayey or loamy nature which contain large boulders of rocks many of which have frequently been brought from a distance, but Boulder Clay may at times contain very few large boulders, and at others be almost entirely made up of

1 The effects of glacial action and the direction of the old ice-sheets in the north of England and Wales have been treated of by Tiddeman, Clifton Ward, Mackintosh, Goodchild, De Rance, and others.

them. In many parts of the Eastern Counties it is to a large extent made up of Chalk.

The term "Till' was first applied in Scotland to the stiff unstratified clays containing angular, subangular, and rounded blocks of rock usually polished and striated, and is often used as synonymous for Boulder Clay: the former term is, however, sometimes restricted to the product of land ice, or of an icesheet, the latter to the same material when re-assorted or washed away and redeposited by marine action assisted by icebergs. The term erratic' is applied to boulders that have travelled long distances from the parent rocks.

In Northumberland and in Holy Island beds of Boulder Clay and gravel have been detected; and in this county and in Durham, according to Prof. Ramsay, the miners, while mining a bed of coal, sometimes find the seam crop out deep underground, against a mass of boulder clay that fills an ancient rocky valley of which the plain above gives no indication.

The distribution of the granitic boulders from Criffel, Eskdale, and Shap Fell (Wastdale Crag), forms an interesting subject.

Wastdale Crag (to quote Dr. Nicholson) has been long known as affording most convincing proofs of the action of glaciers and icebergs in the north of England. The Crag itself is much smoothed and polished, or moutonnéed, and in some places is scored by glacial striations, which have a W.S.W. and E.N.E. direction. The erratic blocks are distributed in great numbers over the country to the south and east of the Crag for great distances: they have been traced over the Pennine chain to the Pass of Stainmoor (1,500 feet) as far as the eastern seaboard of Yorkshire.

Speaking of the Till in North Lancashire, which is the product of an ice-sheet, Mr. Tiddeman has observed that there is abundant evidence that it is not coloured by the rocks

on which it lies, but by the rocks over which it has been pushed; and that it is quite possible, nay certain, that in some areas there may be Till of totally different appearance, colour, and material, deposited side by side, by the same agents, and under the same conditions, at the same time.

In the neighbourhood of Manchester the researches of Messrs. Binney, Hull, and others have shown that the Drift deposits may be divided thus:

Upper Boulder Clay.

Reddish-brown clay with glaciated pebbles and boulders, sometimes containing bands of sand. and showing more or less distinct traces of stratification.

Middle Sand and Fine sands, or gravel composed of waterworn Gravel. pebbles, the whole distinctly stratified. Reddish-brown stiff clay with glaciated pebbles, presenting faint traces of stratification.

Lower Boulder Clay.

All these divisions contain marine shells. (See p. 319.) The thickness of these deposits is sometimes 150 or even 200 feet.

The Boulder Clay contains blocks of granite, syenite, porphyry, slate, &c.1

In the Isle of Man Mr. J. Horne has described the following beds:

Boulder Clay, containing some scratched stones and angular boulders, 6 to 8 feet.

Sands and Gravels, finely stratified with many foreign rocks, evidently a marine deposit, 8 to 10 feet.

Bluish clay, very tough, containing scratched stones, but no large boulders, about 12 feet in thickness: this is the representative of the Scotch Till, and a product of land-ice.

These beds are well exposed about half a mile south of Ramsey, and they are overlaid (to quote Mr. Horne) by a series of well-stratified sands and gravels, which evidently

1 Mr. Mackintosh mentions that in the eastern part of North Wales the boulders are called 'Granite tumblers,' and in Cheshire Marble stones.'

rest on an eroded surface of the boulder clay, and pass upwards into that great series of sands, gravels, and shelly clays which form the cliff from Ramsey to the Point of Ayre. The shelly clays contain marine molluscs. Some of the gravels belong to the Kame series.1

In North Wales there are many scattered drifts: near Llandudno Mr. G. Maw has noticed pockets of chert, white sand, and white clay in the Mountain Limestone; these he thinks may be Pre-Glacial deposits. Mr. Mackintosh has described similar beds near Mold. At Colwyn (Rhos) Bay, and in the Peninsula of Wirral, he has noticed the threefold division of the Drift, which has been made out in Lancashire. At Colwyn the beds are underlaid by a blue clay containing striated stones, which Mr. Mackintosh has traced in places through the West Riding of Yorkshire and Cumberland. He has also described many Eskers in North Wales, Cheshire and Shropshire.

In the drift of Warwickshire, according to the Rev. P. B. Brodie, are boulders of sandstone, quartz pebbles, Chalk and flints, Oolites, Lias, Carboniferous Limestone, pebbles of Lower Silurian [or Cambrian] age containing some remarkable fossils identical with those which occur in similar pebbles in the Trias at Budleigh Salterton in Devonshire.

In the Midland Counties, Nottinghamshire, Derbyshire, Warwickshire, Leicestershire, and Northamptonshire, there

1 The term Kame is used in Scotland (Esker in Ireland and Åsar in Sweden) to denote certain peculiar ridges and mounds of drift which rest on the Boulder Clay and other Glacial Drifts, and regarding whose origin there has been much diversity of opinion. Some geologists maintain that they have been formed in the sea during submergence; others that they were produced by marine agency during the elevation of the area after submergence; some again consider that they are due to the action of subglacial waters (waters flowing underneath land-ice), or that they are morainic accumulations; while yet others have attributed them to torrential or fluviatile action.

are extensive deposits of Drift formed of rocks from many different formations, Chalk, Oolites, Lias, Coal Measures, Millstone Grit, Carboniferous Limestone, &c.

At Annesley, in Nottinghamshire, Mr. Aveline describes the gravel as sometimes cemented together into a breccia, and at Blidworth are some isolated masses popularly known as Druidical remains. These curious blocks were, no doubt, first roughly shaped out by the uncemented gravel having been denuded from around the cemented portions, leaving the latter standing high above the level of the ground. Some of these were afterwards shaped by men into their present forms.

In the Great Ponton cutting on the Great Northern Railway in Lincolnshire (to quote Professor Morris), we see the drift on either side of the cutting buoying up an enormous irregular mass of oolitic rock, through which the cutting has passed. This mass of rock is 430 feet long, and, at its deepest part, 30 feet thick; it is much broken and disturbed, but the parts retain to some extent their relative position, and belong to the lower portion of the Oolitic beds of the district.' He observes that although distinctly isolated, it retains sufficient uniformity of character to lead us to infer that it has not been far removed from its original site. This gigantic boulder is, however, not an isolated case, as other masses of Oolitic rock and Marlstone have been noticed in the district, sometimes of sufficient bulk to be quarried, while in the cliffs on the coast of Norfolk are large masses of Chalk which have been similarly drifted and re-deposited.'

'The following paragraph is taken from the work of Messrs. Conybeare and Phillips: In the fields on the south of Sywell in Northamptonshire, the fragments of Chalk are so abundant as to give the appearance of a regular substratum of that substance, turned up by the plough. In the Philosophical Transactions for 1791 is an account of a Chalk pit found at Redlington in Rutland; which, if correct, must be considered as