the earliest geological times, will probably be many hundred times greater than those now existing of which we have any knowledge; and hence the enormous gaps and chasms in the geological record of extinct forms is not to be wondered at. Yet, notwithstanding these chasms in our knowledge, if evolution is true, there ought to have been, on the whole, progression in all the chief types of life. The higher and more specialised forms should have come into existence later than the lower and more generalised forms; and however fragmentary the portions we possess of the whole tree of life upon the earth, they ought to show us broadly that such a progressive evolution has taken place. We have seen that in some special groups, already referred to, such a progression is clearly visible, and we will now cast a hasty glance over the entire series of fossil forms, in order to see if a similar progression is manifested by them as a whole.
The Progressive Development of Plants.
Ever since fossil plants have been collected and studied, the broad fact has been apparent that the early plants—those of the Coal formation—were mainly cryptogamous, while in the Tertiary deposits the higher flowering plants prevailed. In the intermediate secondary epoch the gymnosperms—cycads and coniferae—formed a prominent part of the vegetation, and as these have usually been held to be a kind of transition form between the flowerless and flowering plants, the geological succession has always, broadly speaking, been in accordance with the theory of evolution. Beyond this, however, the facts were very puzzling. The highest cryptogams—ferns, lycopods, and equisetaceae—appeared suddenly, and in immense profusion in the Coal formation, at which period they attained a development they have never since surpassed or even equalled; while the highest plants—the dicotyledonous and monocotyledonous angiosperms—which now form the bulk of the vegetation of the world, and exhibit the most wonderful modifications of form and structure, were almost unknown till the Tertiary period, when they suddenly appeared in full development, and, for the most part, under the same generic forms as now exist.
During the latter half of the present century, however, great additions have been made to our knowledge of fossil
