The Geological and Chronological Distribution of the Devonian Fossils of Devon and Cornwall

Abstract

The limestones, slates, and associated sandstones of North and South Devon and Cornwall have, as is well known, caused much perplexity as to their real place in the chronological series of the geologist. Thanks, however, to the labours of Professor Sedgwick, Sir R. I. Murchison, Mr. Lonsdale, and others, the problem is now generally admitted to be solved; the rocks in question are the representatives or equivalents of the Old Red Sandstone of Scotland and elsewhere; they belong to what is known as the Devonian age of the world. Some little difficulty, however, exists—or rather once existed—in the way of the full acceptance of this chronology. The rocks of Devonshire are crowded with the remains of invertebrate animals, especially shells, corals, and sponges; whilst the supposed contemporary deposits in Scotland and the adjacent islets are so rich in fossil fish that, in the language of the late Hugh Miller, “Orkney, were the trade once opened up, could supply with ichthyolites, by the ton and the shipload, the museums of the world.” But the fossils characteristic of either of these districts are not found in the other; there are no organic links connecting the two localities. Scotland does not yield the mollusks or zoophytes of Devonshire, nor is there recorded in the latter district more than the faintest trace of the ichthyolitic wealth of the North. Though this fact may still have difficulties connected with it, they have ceased to be chronological, for Sir R. I. Murchison tells us “that the same fossil fishes, of species well known in the middle and upper portions of the Old Red of Scotland, and which in large tracts of Russia lie alone in sandstone, are in many other places found intermixed, in the same bed, with those shells that characterize the group in its slaty and calcareous form in Devonshire, the Rhenish country, and the Boulonnais. This phenomenon, first brought to light in the work on Russia, by myself and colleagues, demonstrates more than any other the identity of deposits of this age, so different in lithological aspect, in Devonshire on the one hand, and central England and Scotland on the other. The fact of this intermixture completely puts an end to all dispute respecting the identification of the central and upper masses at least of the Old Red of Scotland with the calcareous deposits of Devonshire and the Eifel.”