Abstract
THE views expressed in Saporta and Marion's “Evolution des Cryptogames” (reviewed at length in NATURE, vol. xxiv. pp. 73, 558) as to the origin of certain markings commonly met with in palæozoic rocks, has led to a long discussion in which many have taken part, the chief champions on either side being Dr. Nathorst, the distinguished Swedish botanist, and the Marquis de Saporta. Dr. Nathorst maintains that they are tracks left by moving or burrowing animals or other inorganic markings, whilst Saporta holds to his original opinion that very many of them are casts of primæval algæ, of kinds now extinct. Nearly all of these markings are in bas-relief on the under surfaces of slabs as if they were moulds of prints or impressions traced in the ancient muds, thus at first sight greatly favouring Nathorst's view of their origin. Saporta demonstrates on the other hand that this is a by no means uncommon mode of fossilisation among undoubted plants, and when we reflect on the composition of algæ, we shall see that scarcely any other mode of fossilisation among them is possible. A leathery olive green sea-weed lying, on an oozy mud would cause an indentation, and if sub sequently covered up, would keep the old surface from contact with the fresh mud, until it might, under favour able conditions, have become sufficiently hardened to retain the impression. The sea-weed, as most olive weeds do now, if left in water or fresh mud, would eventu ally completely dissolve away, leaving no perceptible organic trace of its presence. The cavity thus left would be filled in at last by the overlying mud, and only a cleavage plane would remain, following the contour of the under side of the weed, and marking its former presence. Sometimes, though rarely, the sea-weed might not decay until a cleavage plane had been established around its entire circumference, without leaving the smallest trace of its internal structure, as we often find is the case with far more resisting cryptogamic stems in the older rocks. This Saporta finds is the case with the Bilobites, one of the most vexed of all the “Organismes problématiques,” and he relies with good reason upon their occasional occurrence in this condition and on their reticulated structure to support his contention that they cannot be mere worm tracks or burrows, and that in point of fact they can be naught but the impressions of primordial algæ.
Les Organismes problématiques des Anciennes Mers.
By the Marquis de Saporta. (Paris: Masson, 1884.)
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G., J. Les Organismes problématiques des Anciennes Mers . Nature 31, 386 (1885). https://doi.org/10.1038/031386a0
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DOI: https://doi.org/10.1038/031386a0