ETHERIDGE — DEVONIAJ^ ROCKS AND FOSSIIS. 653 



latus, one Gasteropod, Acroculia vetusta, and two Polyzoa, Fenestella 

 antiqua and Retepora repisteria, help to unite them : the species of 

 the typical genera, Cyrt'ina, Merista, Rensseleria, Stringocephcdus, 

 &c., all characteristic of the slates of North Devon, are of them- 

 selves weighty and good evidence of pre-Carboniferous times. 



It is, however, singular, and will show how little we yet know 

 of the original conditions and distribution of life over even this one 

 area, that at present we are acquainted with only 3 species that are 

 common to the lower, middle, and upper groups in North Devon 

 and West Somerset ; these are the questionable Fenestella antiqua, 

 the ubiquitous Chonetes Hardrensis, and Streptorhynchus crenistria. 

 These long-lived species all pass the confines of the Upper Devonian, 

 and are abundant in the lower beds of the Carboniferous group. 



This imperfect record can only arise from the very incomplete 

 search which the rocks of this area have undergone, and the little we 

 therefore know of their palseontological contents. No agreement 

 with the Carboniferous strata can be deduced from the presence 

 of these three forms, as no real value can be attached to them; it simply 

 shows that the individuals of the species were abundant, widely dif- 

 fused, and long-lived. It also shows, in the absence of other 

 evidence, that the assemblage of forms which constitute the popula- 

 tion of a given area is peculiar and almost definite. In the pre- 

 sent case, 16 species are known to occur in the Lower Devonian 

 53 in the Middle, and 104 in the Upper Devonian ; and yet, out of 

 these, only the 3 species before named are common to the three di^i- 

 sions, or pass through all three ; and these lived on to the Car- 

 boniferous slates. This, be it remembered, is in North Devon ; these 

 three species necessarily ally the lower or Lynton group with the 

 Barnstaple beds (Carboniferous *) to which they pass ; but these are 

 all : it would therefore appear that, palseontologially, there is no 

 evidence to identify, or hardly to connect, the beds above the Upper 

 Old Red Sandstone of Pickwell Down with the underlying Lynton 

 slates and grits, similarity in lithological conditions being no proof 

 of identity or of synchronous deposition. 



6. Agreement of Foreign Devonian Species with our British Middle 

 and Upper Series in North and South Devon. — We know that 144 

 species are common to the Devonian rocks of England and the Con- 

 tinent, as expressed in the general Table II., p. 616. Taking them 

 at percentage value, we have an agreement of 38 per cent, as being 

 common to the British and European areas ; or, of 3 species which 

 occur in our typical beds, 1 is found in the Rhenish, Belgian, 

 and French taken collectively, — a far closer agreement than that 

 which is recognized as existing between oui' Devonian and the Car- 

 boniferous, which, according to the analysis given in the Table, as is 

 1 to 7, or only 14| per cent, occurring as common to the two 

 formations. This relation and identity of species in two chief areas, 

 so widely separated as are the three Continental from the two British, 

 is to my mind a most valid reason for their contemporaneity and simul- 



* That is, admitting that the Barnstaple beds may be of Carboniferous age. 



