The occurrence of a polished flint implement assigns a date to the uppermost portion of this old land-surface(10). It is impossible within the limits of a small volume to discuss in detail the evidence furnished by the records of the rocks as to the relative antiquity of the different constituents of the present vegetation of Britain. In later chapters a few selected plants are described which are pre-eminently ancient types. Before passing to the consideration of the data on which the geological history of plants is based, brief reference may be made to one of the most interesting and difficult problems of botanical research, namely the history of the British flora. CHAPTER II THE GEOGRAPHICAL DISTRIBUTION OF PLANTS 'No speculation is idle or fruitless that is not opposed to truth or to probability, and which, whilst it co-ordinates a body of well established facts, does so without violence to nature, and with a due regard to the possible results of future discoveries.' Sir Joseph Hooker. In the vegetation of the British Isles the leading _rôle_ is played by that large group to which the term Flowering Plants is frequently applied. This group, including the two sub-divisions Dicotyledons and Monocotyledons, is known by the name Angiosperms, a designation denoting the important fact that the seeds are developed in an ovary or protective seed-case (ἁγγειον, a vessel or box). The fact that these highly elaborated products of development made their appearance, so far as we know, at a comparatively late stage in the history of the plant-world, attests their efficiency as a class and demonstrates the rapidity with which they have overspread the surface of the earth as successful competitors in the struggle for existence. As Darwin wrote in a letter to Sir Joseph Hooker in 1881, 'Nothing is more extraordinary in the history of the vegetable kingdom, as it seems to me, than the _apparently_ very sudden or abrupt development of the higher plants(11).' In another letter (1879) to the same friend we read, 'The rapid development as far as we can judge of all the higher plants within recent geological times is an abominable mystery(12).' Making allowance for the probability, or indeed certainty, that the imperfection of the geological record tends to exaggerate the apparent suddenness of the appearance of this vigorous class, and allowing for the fact that our knowledge of the records of the rocks in which the highest plants first occur is very incomplete, we cannot escape from the conclusion that this recently evolved group spread with amazing rapidity. Various reasons may be suggested in explanation of the dominant position which the Angiosperms hold in the floras of the world. As an instance of their rapid increase during the Cretaceous epoch[1], the period which has furnished the earliest satisfactory records of Flowering Plants, the following statement by an American