Page:The Geologist, volume 5.djvu/31

Rh less varied, the fossils are frequently as numerous individually in the slate as in the limestone.

It must be understood that any one of the ten columns just noticed shows, not the total number of species common to the areas the initials of which stand at its head, but simply the number at once common and restricted to them collectively; thus the second of these columns, headed L.S.D., L.C., shows that five species are common and restricted to Lower South Devon and Lower Cornwall, but in the third column we find one species common to them and also to Lower North Devon, in the fourth one common to them and to Upper North Devon, and in the eighth one found in each of them and also in Upper North Devon and Upper Cornwall; hence there are eight species common to the two areas instanced, five of which are restricted to them collectively, and three not. The same explanation applies to the other areas. The total number of species found in any area will be ascertained by adding the figures in all the columns marked "Peculiar to" and "Common to," at the heads of which the initials of the area are found; thus, for example, a total of forty-seven species of Zoophyta occurs in Lower South Devon, of which forty are not found elsewhere in Devon and Cornwall. Moreover, as the column marked "Species" shows that the two counties have yielded forty-nine species belonging to this class, it is evident that two of the total number have not been met with in Lower South Devon; and so on for the other classes and areas, as is shown in the five columns headed "Totals," and distinguished by the initials of the areas. Ranged according to their peculiar specific fossil wealth the areas stand, in descending order, thus:—Lower South Devon, Upper North Devon, Upper Cornwall, Lower Cornwall, and Lower North Devon; the order is the same when the total number of species found in them is considered, with the single exception that, in that case, Lower North Devon and Lower Cornwall are equal.

Of the three hundred and forty-seven species, sixty-seven are met with in various parts of continental Europe, and seven in North America; six of the latter being included in the European sixty-seven, and one of the six is also found in New South Wales; thus making a total of sixty-eight species common to Devon and Cornwall and districts beyond the British Isles.

Comparatively few of the Devonian fossils of Devon and Cornwall appear to have been derived from the Silurian Fauna; eight species only—just enough to suggest a problem or two—are referable to that earlier period; namely, three Corals, two Brachiopods, two Lamellibranchiates—one from each of the sections Monomyaria and Dimyaria—and one Cephalopod. The three corals are Favosites fibrosa, Emmonsia hemisphærica, and Chonophyllum perfoliatum. The first has been found in Lower Silurian rocks at Landovery, in the upper