*%73-] Present State of the Devonian Question. in 



in the South of Ireland, by a series of shales, grits, and 

 limestones*, with a large suite of fossils, having on the whole 

 a considerable analogy with the still richer associations of 

 marine life in the carboniferous limestone. . . . Near 

 Linton, in North Devon, and south of Plymouth, we may 

 satisfy ourselves of the fact that old red sandstone underlies 

 the Devonian beds. . . . From this series of rocks to the 

 carboniferous strata which succeed the transition is easy, — 

 so easy indeed that, in the opinion of Sir R. Griffith and 

 Mr. Jukes, the whole of the Devonian series may be united 

 with the lowest members of the Irish carboniferous group 

 (yellow sandstone and carboniferous slate). What seems 

 ascertained truth is the close approximation in time, in cha- 

 racter of deposition, and in forms of life, of the South 

 Hibernian and South Welsh rocks ; while the North 

 Devonian strata contain with these a somewhat lower group, 

 not distinctly represented in Wales or Ireland."* 



Whether we regard the Devonian slates as the equivalents 

 of the old red sandstone or of the lower carboniferous rocks, 

 a great change in sedimentary condition must have taken 

 place ; and the question is still perhaps to be decided, 

 whether part of the Devonian rocks are a modified extension 

 of the old red sandstone — a point which appears to take its 

 stand merely on palaeontological evidence — or whether the 

 whole of the fossiliferous Devonian slates and limestones be 

 not of lower carboniferous age, the representatives of the 

 mountain limestone and the lower limestone shale, and of 

 the carboniferous slate and limestone of Ireland. This 

 latter opinion finds the more support when we look, as Mr. 

 Jukes and others have pointed out, to the variations which 

 take place in the carboniferous limestone series when traced 

 through the north of England into Scotland, as well as 

 through the South of Ireland. 



Looking at the culm-measures as representing the true 

 coal-measures, and perhaps also the millstone grit, and that 

 they pass gradually downwards into the Devonian rocks, we 

 may possibly find, in the numerous thin bands of limestone 

 which occur along the junction, some feeble representation 

 of the upper part of the mountain limestone ; then come a 

 series of slates, which must in part represent the mountain 

 limestone, the whole of the lower limestone shale, car- 

 boniferous slate, and perhaps a part of the old red sandstone. 

 Beneath these come beds of the acknowledged type of the 

 old red sandstone. 



* Geology of Oxford and the Valley of the Thames, p. 79. 



