XIII 
THE GEOLOGICAL EVIDENCES OF EVOLUTION 
397 
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 gymnosjAerms—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 develop¬ 
ment 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 Avorld, 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 
