The grasses, in particular, do not appear until the Cretaceous,
and do not show much development until the mid-Tertiary; and
their development seems to be chiefly connected with physical
conditions. The meandering rivers and broad lakes of the
mid-Tertiary would have their fringes of grass and sedge, and, as
the lakes dried up in the vicissitudes of climate, large areas of
grass would be left on their sites. To these primitive prairies
the mammal (not reptile) herbivores would be attracted, with
important results. The consequences to the animals we will
consider presently. The effect on the grasses may be well
understood on the lines so usefully indicated in Dr. Wallace's
book. The incessant cropping, age after age, would check the
growth of the larger and coarser grasses give opportunity to the
smaller and finer, and lead in time to the development of the
grassy plains of the modern world. Thus one more familiar feature
was added to the landscape in the Tertiary Era.
As this fresh green carpet spread over the formerly naked plains,
it began to be enriched with our coloured flowers. There were
large flowers, we saw, on some of the Mesozoic cycads, but their
sober yellows and greens--to judge from their descendants--would
do little to brighten the landscape.
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