Page:The Geologist, volume 5.djvu/45

Rh fore, that the Barnstaple beds are somewhat more modem than those of Petherwin.

We are prepared, by even a slight acquaintance with the geographical distribution of existing organisms, to find that deposits strictly contemporary, lithologically similar, and closely connected geographically, have certain fossils peculiar to each; but, unless we recognize time as a factor, it will be difficult to explain the following striking results in Petherwin and Barnstaple. Together they have yielded as many as one hundred and thirty-one species of fossils, yet have no more than seventeen in common; the fossils belong to forty-six genera, of which twenty-five are confined to one or other of the two areas, having amongst them the rich genus Clymenia, with its eleven species all closely restricted, in Britain, to Petherwin, yet occurring in continental Europe. The remaining twenty-one genera are represented by eighty-six species, but the representatives are rarely identical in the two areas, the peculiar being to the common as 69 to 17, that is, as 4 to 1. Contend that these beds are strictly contemporary, and the facts remain to puzzle; grant but the lapse of time, and, at least, part of the difficulty disappears, and thereby furnishes another argument in favour of the opinion now advocated.

Returning for a moment to Tables X. and XI., it will be seen that the Barnstaple have a smaller number of fossils in common with the Lower Devonian, and even the Petherwin beds, than with the Carboniferous; hence they may be considered as belonging rather to the last than to the Devonian series, or, possibly, may have to be regarded as "passage beds" between them.