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Where was the highly differentiated Sauropsidan fauna of the Trias in Palaeozoic times? The supposition that the Dinosaurian, Crocodilian, Dicynodontian, and Plesiosaurian types were suddenly created at the end of the Permian epoch may be dismissed, without further consideration, as a monstrous and unwarranted assumption.
So much for the evolutionary aspect of the Jurassic vegetation in itself. Slender as the connecting links are, it points clearly enough to a selection of higher types during the Permian revolution from the varied mass of the Carboniferous flora, and it offers in turn a singularly varied and rich group from which a fresh selection may choose yet higher types.
In regions where all the geological deposits, Silurian, Devonian, Carboniferous, Permian, Triassic, etc., are piled one upon another, and we can get a glimpse of their internal relations only where some rent has laid them open, or where their ragged edges, worn away by the abrading action of external influences, expose to view their successive layers, it must, of course, be more difficult to follow their connection.
Davidson on the British Brachiopoda, illustrates, in the first place, the tendency of certain generic forms in this division of the mollusca to be persistent throughout the whole range of geological time yet known to us; for the four genera, Rhynchonella, Crania, Discina, and Lingula, have been traced through the Silurian, Devonian, Carboniferous, Permian, Jurassic, Cretaceous, Tertiary, and Recent periods, and still retain in the existing seas the identical shape and character which they exhibited in the earliest formations.
Secondary Cretaceous 7,200,000 years or Jurassic 3,600,000 " Mesozoic Triassic 2,500,000 " Primary Permian 2,800,000 years or Carboniferous 6,200,000 " Palaeozoic Devonian 8,000,000 " Silurian 5,400,000 " Ordovician 5,400,000 " Cambrian 8,000,000 "
There are important coal-beds in India of Permian age. There are coal-beds of Liassic age in South Hungary and in Texas, and of Jurassic age in Virginia, as well as at Brora in Sutherlandshire; there are coals of Cretaceous age in Moravia, and valuable Miocene Tertiary coals in Hungary and the Austrian Alps. Again, older than the true carboniferous age, are the Silurian anthracites of Co.
In Ayrshire, and in the western parts of Devonshire, beds of felspathic porphyry, felstone and ash are interstratified with strata believed to be of Permian age. In Devonshire these have only recently been recognised by Dr. Irving and the author as of Permian age, the strata consisting of beds of breccia, lying at the base of the New Red Sandstone.
As to this there is no dispute; nor, in fact, about the climate from the Cambrian to the Permian. In the Silurian we have "much to suggest uniformity of climate" in fact, we have just the same evidence for it and in the Devonian, when land-plants abound and afford better evidence, we find the same climatic equality of living things in the most different latitudes.
I confess this is wholly incredible to me. The Permian and the Triassic deposits pass completely into one another; there is no sort of discontinuity answering to an unrecorded "Antetrias;" and, what is more, we have evidence of immensely extensive dry land during the formation of these deposits.
Starting from the high plateau of Utah, and going south toward the canon, we descend a grand geologic stairway, every shelf or tread of which consists of different formations fifty or more miles broad, from the Eocene, at an altitude of over ten thousand feet at the start, across the Cretaceous, the Jurassic, the Triassic, the Permian, to the Carboniferous, which is the bottom or landing of the Grand Canon plateau at an altitude of about five thousand feet.
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