Physical Structure and older stratified Deposits of Devonshire. 663 



semblance in the successive groups of North and South Devon ; and that there 

 is a near resemblance in many of the fossils^ especially the corals. Hence we 

 should provisionally refer them to one system. But as there are no sections 

 connecting them unequivocally with well-ascertained formations, a more exact 

 comparison and place of the several groups must depend on a future examina- 

 tion of the fossils. 



4. Attempting, however, provisionally to bring the groups of North and 

 South Devon into direct comparison, we were first induced to compare the 

 highest calcareous group of North Devon (No. 5.) with the great upper lime- 

 stone of South Devon. The two formations in a part of their range are asso- 

 ciated with red sandstone; several of their fossils approach the carboniferous 

 type, and some of their corals are specifically the same. But we were led to 

 reject this hypothesis, chiefly because it left the great upper group of the 

 South Devon slates (No. 4) entirely unaccounted for in North Devon. 



5. The Ilfracombe calcareous slates very closely resemble (as above stated) 

 some of the upper calcareous slates of Plymouth and Tor Bay. But if we 

 rigidly identify the Ilfracombe limestone with the upper limestone of South 

 Devon, we have the great red arenaceous group of Plymouth entirely unac- 

 counted for in North Devon. On the other hand, the great red arenaceous 

 group of North Devon (No. 2.) is, in its magnitude and general structure, 

 almost identical with the great red arenaceous group over the Plymouth lime- 

 stone. Notwithstanding our distrust of mere mineral characters, we seize on 

 these groups as our best terms of comparison. On that hypothesis, the lower 

 divisions of the South Devon section would be geologically lower than the 

 lowest members of the North Devon section ; (which may be easily admitted 

 when we regard the vast thickness of the descending series between Avon 

 Mouth and Dartmoor (see PI. LI., fig. 5 & 9.)); and the calcareous slates 

 of Linton would be nearly on the parallel of the Plymouth limestone. 



6. Not, however, to push these analogies too far, we would, in a general 

 way, bring the great calcareous and arenaceous series, between the North 

 Devon Foreland and Ilfracombe inclusive, into comparison with the arenaceous 

 and calcareous groups on Plymouth Sound ; on which hypothesis the lower 

 groups of South Devon are unrepresented in North Devon ; and the slate rocks 

 south of the Ilfracombe limestone (group No. 4.) may be compared in a ge- 

 neral way with the great upper slate group of South Devon. 



We throw out these conclusions merely as provisional, and to be confirmed 

 or invalidated by a more complete examination of the organic remains in the 

 several groups. 



