At the close of this period the changes ever taking place transformed the conditions of life in a way the reverse of that which we have hitherto been examining. So far each age has shown an increase of life on the age preceding it. But when the great outburst of carboniferous activity began to wane it was followed by a lessening of the wave of life. As we said in the last chapter, there lie on the top of the coal-bearing strata beds to which the older geologists gave the name of New Red Sandstone. But in 1841 the New Red Sandstone was divided into two distinct geological formations. To the lower and older part Murchison gave in 1841 the name of Permian (from _Perm_ or _Permia_, an ancient kingdom in Russia, where red sandy rocks of this age form nearly all the surface), but in Germany it is more frequently called the Dyas (from Lat. _duo_, two), because in that country it is composed of _two_ well-marked divisions--red sandstones below and magnesian limestones above. Thus there are two types of this Permian formation: the Permian type proper--a mixed series of red sandstones, marls, shales, and limestones, with some thin beds of coal, as found in Russia; and the Dyassic type, as seen in Germany. We do not know what brought about the change: though we do know that during it there was great volcanic activity over Europe and that the waning forests of vegetation and the steaming swamps gave place to desert plains. Vegetation sank lower and lower. The forests disappeared or dwelt only in clusters. The soft sappy trees gave place to hardy pines which clung to the plains and the mountains, and other sterner types began to appear, allied to the spruces, yews, and ginkgo. The ginkgo tree is one of the oldest of the tree type which now has a living representative. Any reader interested enough in the matter to walk along Royal Hospital Road, Chelsea, will find a ginkgo tree just outside the Old Physic Garden; and of course a good many other examples are preserved in botanic gardens. The cycads, offshoots of the ferns, through the strange group of trees known as the cycado-filices, spread through the woods.