You must not think this great river flowed in the Island of England as it is to-day. England was being made then. This must have been part of a great continent in those days, for such a great river to flow through, and form a delta of such size. We cannot tell quite what was the course of this river. But to the north of where we are now must have stretched a great continent, with chains of lofty mountains far away, from which the head waters of the river flowed. Near its mouth the river broke up into many streams, separated by marsh land; while inside the sand banks of the sea shore would be large lagoons as in the Nile delta at the present day. In these waters lived the shellfish whose shells we are finding. And flowing through great forests the river carried down with it logs of wood and whole trees, and left them stuck in the mud near its mouths for us to find to-day. What kind of trees grew in the country the river came from? Well, there were no oaks or beeches, no flowering chestnuts or apples or mays. But there were great forests of coniferous trees; that is trees like our pines and firs, cedars and yews, and araucarias; and there were cycads--a very different kind of tree, but also bearing cones--which you may see in a greenhouse in botanical gardens. They have usually a short trunk, sometimes nearly hemispherical, with leaves like the long leaves of a date palm. They are sometimes called sago trees, for the trunk has a large pith, which, like some palms, gives us sago. Stems of cycads, covered with diamond-shaped scars, where the leaf stalks have dropped off, are found in the Wealden deposits. Most of the wood we find is black and brittle. Some, however, is hard as stone, where the actual substance of the wood has been replaced by silica, preserving beautifully the structure of the wood. Specially noteworthy are fragments of a tree called _Endogenites_ (or _Tempskya_) _erosa_, because it was at first supposed to belong to the endogens,--the class to which the palm bamboo belong; it is now considered to be a tree-fern. Many specimens of this wood are remarkably beautiful, when polished, or in their natural condition. Here, by the way, it may be well to explain how we name animals and plants scientifically. We have English names only for the commoner varieties. So we have to invent names for the greater number of living and extinct animals and plants. And the best way is found to be this. We give a name, generally formed from the Latin--or the Greek--to a group of animals or plants, which closely resemble one another; the group we call a _genus_. Then for the _species_, the particular kind of animal or plant of the group, we add a second name to the first. Thus, if we are studying the apple and pear group of fruit trees, we call the general name of the group _Pyrus_. Then the crab apple is _Pyrus malus_, the wild pear _P. communis_, and so on. So that when you arrange any of your species, and put down the