Page:Quarterly Journal of the Geological Society of London, vol. 26.djvu/162

from the same, has there ever been a case observed where rocks containing Devonian fossils overlie Silurian ones with Silurian fossils, the matrix being the same in both cases^[1]? The question is difficult to answer; but when we examine the contents of these "pebbles" (or "popples," as they are locally designated), it is not easy to suppose them of the same age, if our identification of the fossils is correct, because, so far as I know, in no locality hitherto investigated has such an assemblage been exhibited; but I would again remark that were we not positively assured by Messrs. Rouault, Salter, and De Verneuil that three or four of the Brachiopoda are in reality Lower-Silurian fossils, it would not be very difficult, I think, to refer most of them, if not all, to a single period. None of the rocks known in England have, however, presented a similar fauna; nor have the red sandstone and quartzite beds of May and Fengrolles in Normandy,any more than those described by M. Rouault in Brittany, furnished more than a very small proportion of the species found in the Budleigh pebbles. Mr. Vicary seems, however, to believe that they may have been derived from a nearer source, and that they once formed a beach in the New Bed Sandstone sea, similar to that of the Chesil bank near Portland; but we have no evidence of this that I can collect in the Channel; and even if such a bed did exist, it would not clear away the difficulty connected with the presence of fossils of two distinct periods(?). It has been suggested that a great similarity exists between the Budleigh fossils and those described by Messrs. Ribeiro and Sharpe from the Serra de Bussaco, in Portugal^[2]; but I could not identify with certainty a single species of Brachiopoda as common to the Portuguese locality and that of Budleigh Salterton. It is true that those authors state that the lowest division of the Silurian system in Portugal is composed of quartzites, micaceous sandstones, &c.; but I can hardly suppose that any of the Budleigh boulders were drifted from that locality. A mystery still hangs over the derivation of these boulders, nor can I account for the supposed and extraordinary mixture of Silurian and Devonian forms in the same locality; but I must place a reserve on the above statement, and qualify my meaning—namely, that although in this "remanie" deposit there appears to exist an assemblage of species peculiar to two distinct epochs, this melange does not seem to occur in the same pebble; on the contrary, every individual boulder contains specimens referable either to the one or to the other epoch; so that no melange has been hitherto detected in the same pebble, or existed in the parent rock. It is to my mind quite certain (and I am supported in this opinion by M. de Verneuil) that those boulders which contain Spirifera Verneuilii, Rhynchonella inaurita, Streptorrhynchus crenistria, Productus Vicaryi, Chonetes, &c. are of Devonian age; consequently all other forms that occur in the same mass of rock along with these must necessarily belong to the same period.

1. We all know that conglomerates containing fragments of rock of different ages have been met with in several places. It is the matrix being the same that causes the difficulty.
2. Quart. Journ. Geol. Soc. vol. xx. p. 135, 1853.