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Of course, the collections of living types in any museum must be more numerous than those of fossil forms, for the simple reason that almost the whole of the present surface of the earth, with the animals and plants inhabiting it, is known to us, whereas the deposits of the Silurian and Devonian periods are exposed to view only over comparatively limited tracts and in disconnected regions.
The large deep swamps were best to deal with, because they make a break in the forest, and the sun can come down on their surface and bake a crust, over which you can go, if you go quickly. From experience in Devonian bogs, I knew pace was our best chance, and I fancy I earned one of my nicknames among the Fans on these.
Thus the Devonian Ganoids, though almost all members of the same sub-order as Polypterus, and presenting numerous important resemblances to the existing genus, which possesses biconcave vertebræ, are, for the most part, wholly devoid of ossified vertebral centra.
My Father used to tramp in solitude around and around the red ploughed field which was going to be his lawn, or sheltering himself from the thin Devonian rain, pace up and down the still-naked verandah where blossoming creepers were to be. And I think that there was added to his chagrin with all his fellow mortals a first tincture of that heresy which was to attack him later on.
The fundamental rock is slate or grit of Devonian age, furrowed by numerous valleys, often richly wooded, and diversified by conical hills of trachyte; or by crater-cones, formed of basalt or ashes, sometimes ruptured on one side, and occasionally sending forth streams of lava, as in the cases of the Perlinkopf, the Bausenberg, and the Engelerkopf.
The Devonian rocks may lie at the surface simply because the thousands of feet of carboniferous strata that once lay above them have been worn away. All that the cautious geologist dare assert, therefore, is that the region in question did not become permanent land surface earlier than the Devonian age.
He was no more anxious to insure his own reputation as a liar than to uphold the truthfulness of his companion; and he seemed unaware of what was incongruous in his attitude, and was plainly sincere in both characters. It was not surprising that he should take an interest in the Devonian, for the lad worshipped and served him in love and wonder.
The first three systems were named from the fact that their strata are well displayed in Wales. The Cambrian carries the Roman name of Wales, and the Ordovician and Silurian the names of tribes of ancient Britons which inhabited the same country. The Devonian is named from the English county Devon, where its rocks were early studied.
The Devonian lost heart at so many refusals. He had not the impudence to beg; although, as he said, 'when I had money of my own, I always gave it. It was only on Saturday morning, after three whole days of starvation, that he asked a scone from a milkwoman, who added of her own accord a glass of milk.
Thus the Devonian Ganoids, though almost all members of the same sub-order as 'Polypterus', and presenting numerous important resemblances to the existing genus, which possesses biconcave vertebrae, are, for the most part, wholly devoid of ossified vertebral centra.
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