492 PROCEEDINGS OF THE GEOLOGICAL SOCIETY - . [May 20, 



Nos. 8, 9, 10, the remaining Devonian groups, are not necessary 

 to our purpose. But it is worthy of remark that the fossils quoted 

 by M. Gosselet as having been found by M. Hebert in the Burnot 

 conglomerate are Marwood species (Cucullcea Hardingii. Productus? 

 Murchisonianus, &c), and must have been obtained from other and 

 higher beds. 



It would appear, from all that has been published regarding the 

 Upper Devonian beds of Saxony, the Hartz, Nassau, and Westphalia, 

 that the Marwood beds are absent in these districts, — the Carboni- 

 ferous Limestone resting at once on the Clymenia-limestone, or 

 Petherwin group. 



In the Rhenish provinces, in Belgium, and in the north-west of 

 France, on the contrary, the Marwood group is present. And this 

 variety in the distribution adds strength to the inference already 

 drawn on other grounds, that the Marwood group is unconformable 

 to the other members of the Devonian. The Carboniferous Slate is, 

 as we have seen, only here and there developed to its full extent ; 

 and as we know that the Mountain Limestone itself is universal over 

 the greater part of Europe, and has besides a much wider extension, 

 the reasonable inference would be that, after the filling-up of the 

 sea-bed towards the close of the Devonian period, a continued sub- 

 sidence took place, which allowed the older beds to be gradually 

 covered up successively, first by the Marwood and Pilton group, then 

 by the Carboniferous Slate or Lower Limestone -shale (the terms 

 are convertible), and lastly by the thick masses of the Mountain 

 Limestone itself, which we know in many cases overlaps the whole 

 Devonian series and rests upon the Silurian slates. 



I should scarcely have referred to the North- American area but 

 for the purpose of directing attention to a very interesting point, 

 confirmatory of all that has been said above regarding the age of the 

 uppermost Devonian — the " Chemung group" of the New York series. 



Of this group Professor Hall has given sufficient details in his 

 * Geology of the Fourth District' to enable us to see that its fossils, 

 as a whole, agree well with the Petherwin or Upper Devonian group. 

 It includes several fossils with which we are familiar. Amongst 

 them, Phacops nupera, Hall (P. hufo, var.) ; Aviculopecten, a great 

 many species ; Orthis interlineata ; Spirifer disjimctus, and many 

 others, including S. Urii (S. unguiculus) ; Atrypa reticularis, and 

 many varieties of this variable shell, as in our own Newton-Bushel 

 limestones, e. g. A. dumosa, A. hystrix, A. tenuilineata, <fcc. ; Pe- 

 traia, Ceriopora, &c. ; also Avicula Da?nnoniensis in plenty. This 

 group of species might be easily referred to the Barnstaple group, 

 but it is more agreeable with the whole of the facts to consider it 

 the equivalent of the Petherwin or Clymenia-group, and the fossils 

 are rather in favour of this view. Moreover, Professor Hall lays 



omission is of importance, and may render it possible for No. 5 to be a lower 

 member of the Barnstaple or Pilton group, this is unlikely, as Cardium palma- 

 tum is a characteristic Petherwin species, and rarely, if ever, occurs in the Mar- 

 wood beds. 



