1 873.] Present State of the Devonian Question. 105 



Looking to the origin of the term " Devonian," we learn 

 that Mr. Lonsdale was the first to point out that the cha- 

 racters of the fossils of the Devon limestones seemed to 

 give them an intermediate place between the upper silurian 

 rocks and the mountain limestone, and it was this sug- 

 gestion which in 1839 led Sedgwick and Murchison* to 

 adopt the term " Devonian system " for the series of rocks 

 in North and South Devon which underlie the culm- 

 measures. Henceforth they were regarded as contempora- 

 neous with the old red sandstone. It was even then hinted 

 that possibly the mountain limestone was represented by 

 a part of the culm-measures, and when one refers to the 

 subsequent papers one sees how much room there was to 

 doubt the clearness of this correlation, and in the writings 

 of De la Beche particularly, we find the difficulties attending 

 it fully pointed out.t This is apparent when he compares 

 the Upper Devonian rocks with the upper portion of the old 

 red sandstone, as exhibited at no very great distance apart. 

 For the upper beds of the old red sandstone in South Wales 

 and the Mendip Hills show no similarity whatever to the 

 Upper Devonian rocks. He, moreover, refers to the view 

 taken by Mr. (now Sir Richard) Griffith in 1842, who then 

 pointed out the strong resemblance between the North 

 Devon rocks and those beds in Ireland, which he called 

 carboniferous slate and yellow sandstone, deposits equiva- 

 lent to the transition beds, or lower limestone shale, between 

 the old red sandstone and the mountain limestone. J These 

 views, in facl:, were almost the same as those at which 

 Mr. Jukes arrived. § It was in 1866 that his famous paper 

 was read before the Geological Society of London, || and 

 therein Mr. Jukes brought forward (though not for the first 

 time) the views, which for fifteen years previously he had 

 been thinking over, and which led him to consider the rocks 

 of North Devon to belong partly to the group called carboni- 

 ferous slate in Ireland, and partly to the old red sandstone. 

 He based his interpretation upon an intimate knowledge of 

 the geology of the South of Ireland, where he found that the 

 mountain limestone which was separated from the old red 

 sandstone by the carboniferous slate became in places en- 

 tirely replaced by the slate, so that this slate then filled 



* Trans. Geol. Soc., 2nd Ser., vol. v., p. 633. 

 f Mem. Geol. Survey, vol. i., p. 65. 

 X Idem, p. 76. 



§ Additional Notes on the Grouping of the Rocks of North Devon and 

 West Somerset. 8vo. Dublin, 1867. P. 19. 

 || Quart. Journ. Geol. Soc, vol. xxii., p. 320. 



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