26 



THE GEOLOGIST. 



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 locali- 

 zation had been determined by still earlier conditions ? Eight Silu- 

 rian forms do make tlieir appearance amongst the fossils of Devon 

 and Coniwall — are not these the very organisms ? jS'ow it so happens 

 that they are not. The Silurians spoken of are Favosites Jihrosa, 

 JEmmonsia hemisplKsrica, Chonopliyllum perfoliatmn, Atrypa aspera, 

 A. reticulatiis^ Pterinea ventricosa, Clidophonis ovatus, and Ortho- 

 ceras imhricatum ; whilst the species common to Lower jSTorth and 

 South Devon are Favosites cervicornis, F. diibia, FenesteUa arthritica, 

 String oceplialus Burtini, Sjnrifct^ aperturatus, Sp. Icsvicosta, Ortliis 

 granulosa, and Clionetes sordicla. In fact, there is not one Silurian 

 form recorded amongst the Lower Xorth Devon series. This solu- 

 tion, 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 diflficulties 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 con- 

 temporary deposits of the north and south, and, by its thermal or 

 other qualities, formed an all but iuipeuetrable 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 I3evon and Cornwall ; that of the fifty- 

 eight species which passed over to the next succeeding Fauna, one 

 only occurs in the carboniferous shales of jSTorth Devon, whilst all 

 the others are found in central and northern England, Ireland, Bel- 

 gium, 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, ns 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, " thau the blending 

 of Silurian and Carboniferous corals is of connnon 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 tliey 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 Carbo- 

 niferous, but of an intermediate character. The palieontological 

 argument, then, stands tluis : — There are sixty-six witnesses sup- 

 posed to testify that the rocks are not Devonian, and two hundred 

 and eighty-one — upwards of 4 to 1 — which emphatically declare that 



* Quart. .Tourn. Geol. Soc. vol. xvi. p. xl. 



