Page:The Geologist, volume 5.djvu/43

Rh Petherwin appears to have been richer than Barnstaple in Zoophyta and Cephalopoda, but poorer in Echinodermata and Lamellibranchiata; whilst neither of the areas has yielded any fossil sponges.

Assuming the higher antiquity of the South Devon and contemporary beds—to which, probably, no geologist will object—it follows that the fossils common to it and Petherwin, or Barnstaple, or both, were contributions from it to them. Regarded thus, the populations of the two areas were made up as is shown below.

The term "peculiar," in the table, is meant to denote such species as, in England, are found in Petherwin or Barnstaple only; and "common" to mark those found in both, but not elsewhere in the British Isles; "carboniferous" is used to designate the species common to the deposits of that age and Petherwin, or Barnstaple, or both; exclusive of six found also in Lower Devonian deposits. It may be remarked here that no fossil occurring in South Devon, Petherwin and Barnstaple, appears to have been found in Carboniferous rocks.

The Carboniferous figures 13 and 16 in Table X. are not in addition to the previous numbers in the Table; the totals—72 and 76 respectively—are, of course, complete without them.

In order to show the relative value of the figures just given, the following Table has been calculated on the method of putting each total 72 and 76 equal to 1000, and equating the other figures in Table X. to it. It should be remembered, however, that whilst this furnishes better data for comparison, it considerably magnifies the facts.

The Silurian figures are, of course, quite valueless further than as