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Come down the stream of time several millions of years to our own geologic age and we find the earth swarming with the human species like an ant-hill with ants, and with a vast number of forms not found in the Mesozoic era; and the men are doing to a large part of the earth what the ants do to a square rod of its surface. Where did they come from?
Flying reptiles also evolved, to set an example for the bats of the mammalian class, for both kinds of flying organisms converted their anterior limbs into wings, although in different ways. During the Triassic and Jurassic periods of the Mesozoic age, the first birds and mammals appeared to follow out their diverging and independent lines of descent.
Turning to the animal kingdom, he affirmed the tabulate corals of the Silurian rocks to be wonderfully like those which now exist; while even the families of the Aporosa were all represented in the older Mesozoic rocks. Among the Molluska similar facts were adduced.
But if we now cross the frontier between the Cainozoic and the Mesozoic faunae, as they are preserved within the Arctogaeal area, we meet with an astounding change, and what appears to be a complete and unmistakable break in the line of biological continuity.
Hence, if a gradual shifting of the deep sea, which at present bars migration between the easternmost of these islands and America, took place to the westward, while the American side of the sea-bottom was gradually upheaved, the palaeontologist of the future would find, over the Pacific area, exactly such a change as I am supposing to have occurred in the North-Atlantic area at the close of the Mesozoic period.
The discovery in 1855, in the Hastings beds of the Isle of Wight, of Gyrogonites, or spore-vessels of the Chara, was the first example of that genus of plants, so common in the tertiary strata, being found in a Secondary or Mesozoic rock. The Purbeck Beds a Member of the Jurassic Group. Subdivisions of that Group. Physical Geography of the Oolite in England and France. Upper Oolite. Purbeck Beds.
The ancestors of our race during this period were at first represented by true fishes, then by dipneusts and amphibia, and finally by the earliest Amniotes, or the Protamniotes. The third chief section of the organic history of the earth is the Mesozoic or Secondary period. This again is subdivided into three divisions Triassic, Jurassic, and Cretaceous.
A vast ridge rises along the whole western front of the continent, lifting and draining it, from Alaska to Cape Horn. It is the beginning of the Rocky Mountains and the Andes. Even during the Cretaceous period there had been rich forests of Mesozoic vegetation covering about a hundred thousand square miles in the Rocky Mountains region. Europe and America now begin to show their modern contours.
Besides these four tests it may be said, in a general way, that volcanic rocks of Primary or Palaeozoic antiquity differ from those of the Secondary or Mesozoic age, and these again from the Tertiary and Recent.
I say the survival of the fit; there are degrees of fitness in the scale of life; the fit survive, and the fittest lead and dominate, as did the reptiles in Mesozoic time, and the mammals in Tertiary time. Among the mammals man is dominant because he is the fittest. Nations break up or become extinct when they are no longer fit, or equal to the exigencies of the struggles of life.
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