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Updated: June 2, 2025
So complete is the sequence, that the plate on which their embryonic changes are illustrated contains more than thirty figures, all representing different phases of their growth. There is not a living Crab represented so fully in any of our scientific works as is that one species of Trilobite whose whole story Barrande has traced from the egg to its adult size.
I see nothing whatever against the supposition that distributional provinces of terrestrial life existed in the Devonian epoch, inasmuch as M. Barrande has proved that they existed much earlier.
We see this in the plainest manner by the fact that all the most eminent palæontologists, namely Cuvier, Agassiz, Barrande, Falconer, E. Forbes, &c., and all our greatest geologists, as Lyell, Murchison, Sedgwick, &c., have unanimously, often vehemently, maintained the immutability of species.
The strongest apparent exception to this latter rule, is that of the so-called "colonies" of M. Barrande, which intrude for a period in the midst of an older formation, and then allow the pre-existing fauna to reappear; but Lyell's explanation, namely, that it is a case of temporary migration from a distinct geographical province, seems to me satisfactory.
The old notion of all the inhabitants of the earth having been swept away at successive periods by catastrophes, is very generally given up, even by those geologists, as Elie de Beaumont, Murchison, Barrande, etc., whose general views would naturally lead them to this conclusion.
M. Barrande pointed out that these primordial trilobites have a peculiar facies of their own dependent on the multiplication of their thoracic segments and the diminution of their caudal shield or pygidium.
Cephalopoda have not yet been found lower than this group, but it will be observed that they occur here associated with genera of Trilobites considered by Barrande as characteristically Primordial, some of which belong to all the divisions of the British Cambrian about to be mentioned. This renders the absence of cephalopoda of less importance as bearing on the theory of development.
We should not forget that only a small portion of the world is known with accuracy. M. Barrande has lately added another and lower stage to the Silurian system, abounding with new and peculiar species. Traces of life have been detected in the Longmynd beds beneath Barrande's so-called primordial zone.
These peculiar genera were afterwards found in rocks holding a corresponding position in Wales, and I shall retain for them the term Cambrian, as recent discoveries in our own country seem to carry the first fauna of Barrande, or his primordial type, even into older strata than any which he found to be fossiliferous in Bohemia.
Classification of the Cambrian Group, and its Equivalent in Bohemia. Upper Cambrian Rocks. Tremadoc Slates and their Fossils. Lingula Flags. Lower Cambrian Rocks. Menevian Beds. Longmynd Group. Harlech Grits with large Trilobites. Llanberis Slates. Cambrian Rocks of Bohemia. Primordial Zone of Barrande. Metamorphosis of Trilobites. Cambrian Rocks of Sweden and Norway.
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