glaciers may be traced; Blocs perchés are found in most valleys in the Lake District and North Wales, while grooved and polished rock-surfaces and striated stones have been detected in many places. In some of the low-lands are deposits of distant origin which cannot have been accumulated by rain and rivers, nor have been formed unaided by marine action.

In 1831 Mr. J. Trimmer detected traces of stratified drift containing marine shells at a height of 1,300 feet on Moel Tryfaen, which indicated a submergence to this extent in Post-Pliocene times; and in 1842 Dr. Buckland recognized the former existence of glaciers in many parts of North Wales.

Since this period the subject has been very extensively studied, and the general conclusions may be stated to be, that during what is called the Glacial period the northern parts of England and Wales were covered with ice ;—(to quote Prof. Ramsay) 'the average level of the land may then have been higher than at present, by elevation of the whole, and a little because it had not suffered so much degradation: but whether this was so or not, the mountains and much of the low-lands were covered with a universal coating of ice, probably as thick as that in the north of Greenland in the present day.

Small glaciers were locally formed on the Snowdonian and Cumbrian hills. During the time that

• these great results were being produced by glacial action, there were occasional important oscillations in temperature, so that the ice sometimes increased and sometimes diminished, and land animals that lived habitually in more temperate regions, at intervals advanced north or retreated south with the retreating or advancing ice. At length, however, a slow subinersion of the land took place.'

During the time when the lands in North Wales and the north of England were covered with ice, it has been conjectured

that the southern tracts of Wales and England were submerged, and then material extruded by the glaciers was dispersed over the submerged country, while ice-bergs may have given their contributions to the drifts that are scattered over the country. The subsequent period of greater submergence, which in Wales was more than 1,300 feet, was attended by the dispersion and deposition of more material.

Again the land rose, and glaciers were formed in North Wales and in the Lake District. Those who visit North Wales should carry Prof. Ramsay's Old Glaciers of Switzerland and North Wales' in their pockets. With this guide the many obvious facts will be understood even by those who have never seen a glacier--the old records of glacial action are as certainly marked on the rocks and in the vallers, as is the hand of man in the hieroglyphics on ancient monuments.

This is but a feeble sketch of the great changes indicated during the Glacial period, but it would be impossible here to do justice in so small a space as must be allotted to the subject, and those who would pursue the subject further should consult Mr. James Geikie's “Great Ice Age.'

It may, however, be useful to give the following summary by Mr. Geikie of the great changes that occurred over the British Islands in the Quaternary period :1. Indications of approaching cold are met with in the Newer Pliocene

deposits. 2. Intense glacial conditions, with great confluent glaciers ; inter

mediate mild, and warm periods; arctic and southern mammalia visit Britain alternately, according as climatal conditions become

suited to their needs. 3. Disappearance of arctic conditions. Britain continental, with cli

mate changing from cold to temperate and genial, and again to temperate. In early stages of continental conditions the arctic man malia invade Britain; subsequently these disappear, and are succeeded by the hippopotamus, and other southern forms.

1 This Summary, which has been kindly furnished to me by Mr. Geikie, represents the views which are set forth in the New Edition of his work.

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-tem

perate, 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.

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 distri. buted 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 bas 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 :

Reddish-brown clay with glaciated pebbles and Upper Boulder Clay.

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. Lower Boulder Clay.

Reddish-brown stiil' clay with glaciated pebbles,

presenting faint traces of stratification. 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.'

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.'

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