transformations date from the period of Arctic cold, which caused ice of enormous thickness to form over the whole of north-western Europe.

Throughout this momentous age in the history of Yorkshire, as far as we can tell, the flaming sunsets that dyed the ice and snow with crimson were reflected in no human eyes. In those far-off times, when the sun was younger and his majesty more imposing than at the present day, we may imagine a herd of reindeer or a solitary bear standing upon some ice-covered height and staring wonderingly at the blood-red globe as it neared the horizon. The tremendous silence that brooded over the face of the land was seldom broken save by the roar of the torrents, the reverberating boom of splitting ice, or the whistling and shrieking of the wind.

The evidences in favour of this glacial period are too apparent to allow of any contradiction; but although geologists agree as to its existence, they do not find it easy to absolutely determine its date or its causes.

Croll's theory of the eccentricity of the Earth's orbit¹ as the chief factor in the great changes of the Earth's climate has now been to a great extent abandoned, and the approximate date of the Glacial Epoch of between 240,000 and 80,000 years ago is thus correspondingly discredited by many geologists. Professor Kendall inclines to the belief that not more than 25,000 years have elapsed since the departure of the ice from Yorkshire, the freshness of all the traces of glaciation being incompatible with a long period of post-glacial time.

¹ "Climate and Time." James Croll, 1889.

The superficial alterations in the appearance of these parts of Yorkshire were brought about by the huge glaciers which, at that time, choked up most of the valleys and spread themselves over the watersheds of the land.

In the warmer seasons of the year, when the Arctic cold relaxed to some extent, fierce torrents would rush down every available depression, sweeping along great quantities of detritus and boulders sawn off and carried sometimes for great distances by the slow-moving glaciers. The grinding, tearing and cannonading of these streams cut out courses for themselves wherever they went. In some cases the stream would occupy an existing hollow or old water-course, deepening and widening it, but in many instances where the ice blocked a valley the water would form lakes along the edge of the glacier, and overflowing across a succession of hill shoulders, would cut deep notches on the rocky slopes.

Owing to the careful work of Mr C.E. Fox-Strangways and of Professor Percy F. Kendall, we are able to tell, almost down to details, what took place in the Vale of Pickering and on the adjacent hills during this period.

In the map reproduced here we can see the limits of the ice during the period of its greatest extension. The great ice-sheet of the North Sea had jammed itself along the Yorkshire coast, covering the lower hills with glaciers, thus preventing the natural drainage of the ice-free country inland. The Derwent carrying off the water from some of these hills found its outlet gradually blocked by the advancing lobe of a glacier, and the water having accumulated into a lake (named after Hackness in the map), overflowed along the edge of the ice into the broad alluvial plain now called the Vale of Pickering. Up to a considerable height, probably about 200 feet, the drainage of the Derwent and the other streams flowing into the Vale was imprisoned, and thus Pickering Lake was formed.

The boulder clay at the seaward end of the Vale seems to have been capped by ice of a thickness of nearly 100 feet which efficiently contained the waters of the lake until they overflowed through a depression among the hills to the south of Malton. If the waters escaped by any other outlet to the west near Gilling and Coxwold, it can scarcely have been more than a temporary affair compared to the overflow that produced the gorge at Kirkham Abbey, as the Gilling Gap was itself closed by the great glacier descending the Vale of York. The overflow of the lake by this route, south of Malton, must have worn a channel down to a lower level than 130 feet O.D. before the ice retreated from the seaward end of the Vale, otherwise the escape would have taken place over the low hills blocking the valley in that direction and the normal course of the drainage of the country would have been resumed. The southern overflow evidently dug its way through the hills fast enough to maintain that outlet, and at the present time the narrow gorge at Kirkham Abbey is only 50 feet above sea level, and the hills through which the Derwent passes at this point are from 200 to 225 feet high.

As the waters of the lake gradually drained away, the Vale was left in a marshy state until the rivers gradually formed channels for themselves. In recent times drainage canals have been cut and the streams embanked, so that there is little to remind one of the existence of the lake save for the hamlet still known as The Marishes. The name is quite obviously a corruption of marshes, for this form is still in use in these parts, but it is interesting to know that Milton spelt the word in the same way as the name of this village, and in Ezekiel xlvii. II we find: "But the miry places thereof, and the marishes thereof, shall not be healed." The ease with which a lake could again be formed in the Vale was demonstrated in October 1903 after the phenomenally wet summer and autumn of that year, by a flood that covered the fields for miles and in several places half submerged the hedges and washed away the corn stooks.

The evidence in favour of the existence of Lake Pickering is so ample that, according to Professor Kendall, it may be placed "among the well-established facts of glacial geology."¹

¹ Quarterly Journal of the Geological Society, vol. lviii. part 3, No. 231, p. 501.

We have thus an accredited explanation for the extraordinary behaviour of the river Derwent and its tributaries, including practically the whole of the drainage south of the Esk, which instead of taking the obviously simple and direct course to the sea, flow in the opposite direction to the slope of the rocks and the grain of the country. After passing through the ravine at Kirkham Abbey the stream eventually mingles with the Ouse, and thus finds its way to the Humber.

The splendid cañon to the north of Pickering, known as Newton Dale, with its precipitous sides rising to a height of 300 or even 400 feet, must have assumed its present proportions principally during the glacial period when it formed an overflow valley from a lake held up by ice in the neighbourhood of Fen Bogs and Eller Beck. This great gorge is tenanted at the present time by Pickering Beck, an exceedingly small stream, which now carries off all the surface drainage and must therefore be only remotely related to its great precursor that carved this enormous trench out of the limestone tableland. Compared to the torrential rushes of water carrying along huge quantities of gravel and boulders that must have flowed from the lake at the upper end, Newton Dale can almost be considered a dry and abandoned