Page:The Geologist, volume 5.djvu/40

26 other—eight proofs, then, that a passage did exist, unless we suppose that both areas were tenanted from some more distant centre or centres of organic dispersion. It may be asked, were not these eight remnants of an older—a Silurian—fauna, forms of life whose localization had been determined by still earlier conditions? Eight Silurian forms do make their appearance amongst the fossils of Devon and Cornwall—are not these the very organisms? Now it so happens that they are not. The Silurians spoken of are Favosites fibrosa, Emmonsia hemisphærica, Chonophyllum perfoliatum, Atrypa aspera, A. reticulatus, Pterinea ventricosa, Clidophorus ovatus, and Orthoceras imbricatum; whilst the species common to Lower North and South Devon are Favosites cervicornis, F. dubia, Fenestella arthritica, Stringocephalus Burtini, Spirifer aperturatus, ''Sp. Iævicosta, Orthis granulosa, and Chonetes sordida''. In fact, there is not one Silurian form recorded amongst the Lower North Devon series. This solution, therefore, does not seem available. Shall we hold with Professor Phillips that "this unequal diffusion of definite forms of life may often be ascribed to oceanic currents"? I cannot but think that fewer difficulties attach to this than to any other hypothesis which has been proposed; it simply requires us to suppose that a persistent oceanic stream, flowing through central Devon, separated the contemporary deposits of the north and south, and, by its thermal or other qualities, formed an all but impenetrable barrier to the marine tribes. Moreover, whilst it would account for the limited organic distribution we are considering, it would not be out of keeping with the facts that a comparatively great number of species were common to continental Europe and Devon and Cornwall; that of the fifty-eight species which passed over to the next succeeding Fauna, one only occurs in the carboniferous shales of North Devon, whilst all the others are found in central and northern England, Ireland, Belgium, Russia, and other distant localities; and that a comparatively great number of forms are common to the upper areas of Cornwall and North Devon.

Though, as we have seen, the test entirely fails, at least so far as Devonshire is concerned, on which scepticism respecting the existence of a Devonian period has been founded, namely, "that the blending of Silurian and Carboniferous corals is of common occurrence," yet if the word "fossil" is substituted for "coral," a blending of the kind certainly does occur, and doubtless the fact is not without a meaning. Eight species from the preceding period, and fifty-eight from the succeeding—a total of sixty-six—meet in Devon and Cornwall. Are they so many proofs that the rocks in which they were inhumed are not Devonian? It must be borne in mind that there are two hundred and eighty-one species that are neither Silurian nor Carboniferous, but of an intermediate character. The palæontological argument, then, stands thus:—There are sixty-six witnesses supposed to testify that the rocks are not Devonian, and two hundred and eighty-one—upwards of 4 to 1—which emphatically declare that