The Tertiary epoch is just as meagrely represented as the Secondary. Yet this is the period which in other parts of the world possesses records of the most ample kind. The Alps, the Caucasus, the Himalayas were all upheaved in Tertiary times; but of any corresponding activity in the north-east of Scotland, there is no trace. It is only when the Tertiary merges in the Quaternary period that the history is resumed. The deposits of the Ice Age, when Scotland was under the grip of an arctic climate, are much in evidence all over the county and have already been referred to. It is necessary to treat the subject in some detail. During the glacial period, the snow and ice accumulated on the west side of the country, and overflowed into Aberdeenshire. There were several invasions owing to the recurrence of periods of more genial temperature when the ice-sheet dwindled. One of the earlier inroads probably brought with it the chalk flints now found west of Buchan Ness; another brought boulders from the district of Moray. South of Peterhead a drift of a different character took place. Most of Slains and Cruden as well as Ellon, Foveran, and Belhelvie are covered with a reddish clay with round red pebbles like those of the Old Red Sandstone. This points to an invasion of the ice-sheet from Kincardine, where such deposits are rife. Dark blue clay came from the west, red clay from the south, and in some parts they met and intermixed as at St Fergus. A probable third source of glacial remains is Scandinavia. In the Ice Age Britain was part of the continental mainland, the shallow North Sea having been formed at a subsequent period. The low-lying land at the north-east of the county was the hollow to which the glaciers gravitated from west and south and east, leaving their _débris_ on the surface when the ice disappeared. So much is this a feature of Buchan that one well-known geologist has humorously described it as the riddling heap of creation. Both the red and the blue clay are often buried under the coarse earthy matter and rough stones that formed the residuum of the last sheet of ice. This has greatly increased the difficulty of clearing the land for cultivation. Moreover a clay subsoil of this kind, which forms a hard bottom pan that water cannot percolate through, is not conducive to successful farming. Drainage is difficult but absolutely necessary before good crops will be produced. Both difficulties have been successfully overcome by the Aberdeenshire agriculturist, but only by dint of great expenditure of time and labour and money.