The Rein-deer.—We here arrive at a species which must be considered analogical and extinct. The bones were found in abundance near Etampes, in France, in a sand, of which the geological characters do not seem to have been properly ascertained. While these bones were supposed to resemble those of the rein-deer, the size was only that of the roe.
In Scania there have been found some horns of deer, in peat, which are supposed not to be referable to any known species : and it is said that bones of the antelope are found among those of Gibraltar.
The Elk.—The last of the deer tribe is the fossil elk, so abundant in Ireland and in the Isle of Man, and which also occurs in England, and in different parts of Germa ny and France. It seems now to be agreed that it is an extinct species. It cannot, however, in all cases at least, be of very high antiquity; because in Ireland, as elsewhere, it has often been found in peat, and in those beds of su perficial and recent marl already noticed. As the nature of these deposits has been often much misunderstood, and as they have sometimes been referred to a much higher antiquity than they are entitled to, it will be useful here to describe their real nature in as few words as pos sible.
The filling up and consequent obliteration of lakes is one of those great and steady operations in nature which is eternally in progress, and which tends in time to reduce all interior land to a state of dryness, and to render the passage of a river simple and uninterrupted, from its sources to its estuary in the sea. As long, however, as a passes through a lake,. as the Rhone, for''example, does through that of Geneva, the first estuary of such a stream is that lake, and the sea is only a secondary one. Hence the lake detains all those alluvial matters carried down by the river, which lie between that and its sources. In that case, where the stream terminates altogether in the lake, or there is no corresponding issue, an instance of which is afforded by the \Volga and the Caspian, this receptacle is its 'sole estuary. Now the same circum stances precisely apply to every case where there is any depression of land, however small, in which water can lodge ; and thus in mountainous countries, like Ireland, or our own part of Great Britain, we have examples of cavities, containing what may be called pools rather than lakes, some resembling one, and others the other, of the two varieties just mentioned. These, in a corresponding
manner, therefore, become filled up, till the land is reduc ed to an uniform level, and, of course, in some measure by means of the materials which are deposited in them by the streams or the drainage by which they are fed. These alluvial deposits, limited to a• certain extent of sand, gravel, and mud, may be of the most recent possible formation. Where such places are subject to the frequent effects of mountain torrents, the deposits, and the conse quent filling up, proceed with unusual rapidity.
But this is not the only cause which aids in the exclu sion of water from such cavities, and which therefore assists in levelling the land. Many fresh-water shells breed in such lakes, and even in the shallowest and small est pools ; and as their death and reproduction is very rapid in many cases, a considerable addition of solid matter is made to that which is brought in from the rocks and soil which the feeding waters act on in their courses. Such shells, therefore,preduce calcareous beds, which are never, or rarely at least, much consolidated, but are known by the name of marl : a term unfortunately ap plied to ancient deposits, and to rocks belonging to the system of the secondary strata. That marl also varies in character; as the shells may have disappeared entirely, or it may be further intermixed with the clay or the sand introduced by the rivers. In these latter cases it often forms strata, scarcely to be distinguished from some of the ancient marls which belong to the proper system of the rocky strata.
In the last place, the whole becomes covered either with peat or with the ordinary vegetable soil, according to the nature of the ground and the climate ; and thus, except to an experienced eye, it is scarcely discovered or conjec tured that such a lake ever existed. Thus, under all these circumstances, such strata, even when of very modern origin, may be, as they have been, confounded with those of far higher antiquity, which belong to the system of the stratified rocks, and more particularly with those which belong to the basins, such as those of Paris and the Isle of Wight, that follow the last of the general se condary strata, and which form a kind of connecting link between those two kinds of distinct deposits.