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Updated: May 24, 2025
These are regarded as surviving specimens of various groups of animals which, in early times, fell between the Invertebrate and Vertebrate worlds, and illustrate the transition. With their aid a genealogical tree was constructed for the fish. It was assumed that some Cambrian or Silurian Annelid obtained this stiffening rod of cartilage.
From the primitive fishes or Selachii, the earliest Gnathostomes, was developed the legion of the Ganoids. On the other hand, we have a great variety of specimens of this group in the fossil state, from the Upper Silurian onward. Some of these fossil Ganoids approach closely to the Selachii; others are nearer to the Dipneusts; others again represent a transition to the Teleostei.
The trilobites, a quite highly organized order of crustacea, appear in the strata of the silurian epoch almost suddenly, in very many and very distinctly marked species. The uncertainty of our knowledge shows itself most clearly when we ask for the geneologic relationship of the vertebrates. In Chap.
Even at three thousand feet he gave me a chill.... But let Whinney speak. "It is plain," he said, "that the basalt monadnock on which we stand is a carboniferous upthrust of metamorphosed schists, shales and conglomerate, probably Mesozoic or at least early Silurian." At this point our wives burst into laughter. In fact, their attitude throughout was trying but Whinney bravely proceeded.
The Silurian system, the Devonian system, the Carboniferous system, etc., are set down in our books as groups of formations which everywhere succeed each other in a given order; and are severally everywhere of the same age. Though it may not be asserted that these successive systems are universal; yet it seems to be tacitly assumed that they are.
In this reform they were aided by a suggestion of Mr. Lonsdale, who, after studying the Devonshire fossils, perceived that they belonged to a peculiar palaeontological type of intermediate character between the Carboniferous and Silurian.
For these strata Sir Roderick Murchison first proposed the name of Silurian when he had studied and classified them in that part of Wales and some of the contiguous counties of England which once constituted the kingdom of the Silures, a tribe of ancient Britons.
Gold has now been detected in almost every kind of rock, in slate, quartzite, sandstone, limestone, granite, and serpentine, both in veins and in the rocks themselves at short distances from the veins. In Australia it has been worked successfully not only in alluvium, but in vein-stones in the native rock, generally consisting of Silurian shales and slates. Mr.
The gravel outside, at least, is an old friend; it consists of broken bits of gray Silurian rock, and white quartz among it; and one touch of Siluria makes the whole world kin. But there the kindred ends. A few green weeds, looking just like English ones, peep up through the gravel.
In the Silurian epoch following the Azoic we have the first beach on which any life stirred; it extended along the base of the Azoic beds, widening by its extensive deposits the narrow strip of land already upheaved. I propose in my next article to invite my readers to a stroll with me along that beach. Ancient history is forever indispensable to the speculative historian.
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