660 PEOCEEDINGS OP THE aEOLOGICAL SOCIETY. 



nothing- of wliat I believe to be the case, that hardly a single 

 species will ever be found common to the two areas. The very 

 band of Upper Old Eed Sandstone which stretches (in place) across 

 ISTorth Devon from Pickwell Down (Morte Bay) to Wiveliscombe and 

 the Qnantock Hills constitutes a natural base-line to the Upper De- 

 vonian rocks and species. The physical changes that accompanied 

 and produced that great accumulation of red sandstone also seem to 

 have modified the forms of life that succeeded it, now enabling us to 

 draw both a physical and palseontological boundary-line between the 

 well-marked Ilfracombe or Middle Devonian group below, and the 

 Upper, or Baggy and Marwood, group above ; and, more important 

 still, the species comprising the Petherwin fauna to the south of the 

 Culm-trough, which are older in time than those of the Baggy and 

 Marwood beds, have to be interpolated and accounted for, although 

 at present not yet recognized below the Baggy series on the north 

 side of the Culm series. To still carry on our analysis as to the 

 value of the Brachiopoda, and the relationship between the admitted 

 Lower and Middle Devonian rocks of this area and the supposed Car- 

 boniferous Slates south of Yention and Morte Bay, we must state the 

 evidence collected and given in Tables IX. and X. It is there seen that, 

 of the 48 species of this class distributed through the Lower, Middle, 

 and Upper Devonian slates and limestones, only 13 species of the 

 whole are common to the two formations, namely the 9 following : — 



Athyris oblonga, Sow. 

 Piscina nitida, Thill. 

 Lingula squamiformis, Thill. 

 Productus scabriculus, Martin. 

 Khynchonella acuminata, Martin. 



Ehynchonella reniformis, 8( 

 Spirifera Urei, Fleming. 

 Spiriferina insculpta, Thill, 

 Terebratula sacculus, Mart. 



all of which are Upper-Devonian and Carboniferous forms, and not 

 known in older beds north of the Pickwell or Morte-Bay Old Eed 

 Sandstones ; and the remaining 4, 



Ehynckonella pleurodon. I Strep torhynchus creni stria. 



— — pugnus. j Strophomena rhomboidalis. 



are common to the Middle and Upper Devonian and Carboniferous 

 rocks of l^orth Devon ; but if the remaining form, CJionetes sordida, 

 Sow., of the Lower or Lynton Group, and the Clionetes Hardrensis, 

 PhiU., be one species, then lue have only one sJieJl that 'passes through 

 the luhole of the rocJcs of North Devon, or only one species connecting 

 the Upper Devonian slates of Baggy and Marwood, &c. &c., with 

 those of the Lower at Lynton and the Middle at Ilfracombe. The 

 9 Upper-Devonian forms before named have ever been regarded 

 as passage-species, and subject to the caprice and views of those 

 who would (all other evidence wanting) place them either at the 

 base of the Carboniferous, or at the top of the Upper Devonian, 

 although careful examination into their specific value would de- 

 termine them (at least 3 of the 9) as having far greater afiinity 

 with Devonian types, and but a slight range into the Carboni- 

 ferous series. The paucity of species, in all the other zoological 

 groups that exist in common in the Devonian and Carboniferous, 



