As the Devonian period progressed the sea gained on the land, and must have restricted the growth of vegetation, but as the lake deposits now preserve the remains of the plants which grow down to their shores, or are washed into them, we are enabled to restore the complexion of the landscape. Ferns, generally of a primitive and generalised character, abound, and include the ferns such as we find in warm countries to-day. Horsetails and Club-mosses already grow into forest-trees. There are even seed-bearing ferns, which give promise of the higher plants to come, but as yet nothing approaching our flower and fruit-bearing trees has appeared. There is as yet no certain indication of the presence of Conifers. It is a sombre and monotonous vegetation, unlike any to be found in any climate to-day. We will look more closely into its nature presently. First let us see how these primitive types of plants come to form the immense forests which are recorded in our coal-beds. Dr. Russel Wallace has lately represented these forests, which have, we shall see, had a most important influence on the development of life, as somewhat mysterious in their origin. If, however, we again consult the geologist as to the changes which were taking place in the distribution of land and water, we find a quite natural explanation. Indeed, there are now distinguished geologists (e.g. Professor Chamberlin) who doubt if the Coal-forests were so exceptionally luxuriant as is generally believed. They think that the vegetation may not have been more dense than in some other ages, but that there may have been exceptionally good conditions for preserving the dead trees. We shall see that there were; but, on the whole, it seems probable that during some hundreds of thousands of years remarkably dense forests covered enormous stretches of the earth's surface, from the Arctic to the Antarctic.