DEVONIAN OF SEDGWICK AND MURCHISON 253 



ter, might well induce the earlier geologists to class them as among the very oldest 

 deposits of the British Isles. In truth, the southwestern extremity of England 

 presented apparently no regular sedimentary succession, by which its gray, slaty 

 schists, marble limestones, and silicious sandstones could be connected with any 

 one of the British deposits the age of which was well ascertained. The establish- 

 ment of the Silurian system, and the proofs it afforded of the entire separation of 

 its fossils from those of the Carboniferous era, was the first step which led to a 

 right understanding of the age of these deposits. The next was the proof obtained 

 by Professor Sedgwick and myself, that the 'culm measures' of Devon were truly 

 of the age of the Carboniferous limestone, and that they graduated downwards 

 into some of the slaty rocks of this region. Hence, in the sequel it became mani- 

 fest, that the rocks, now under consideration, were the immediate and natural pre- 

 cursors of the coal era, and stood therefore in the place of the Old Red Sandstone 

 of other regions. The highly important deduction, however, of Mr Lonsdale, that 

 the fossils of the South Devon limestones, as collected by Austen and others, really 

 exhibited a character intermediate between those of the Silurian system and of 

 the Carboniferous limestone, was the most cogent reason which induced Professor 

 Sedgwick and myself (after identifying North and South Devon) to propose the 

 term Devonian.* The inference that the stratified rocks of Devonshire and Corn- 

 wall, though of such varied composition, are really the equivalents of the Old Red 

 Sandstone in the regions alluded to has since, indeed, been amply, supported and 

 extended by the researches of Sir Henry De la Beche, Professor Phillips, and many 

 other good geologists. f 



"The most instructive of the sections published by my colleague and myself to 

 illustrate the general structure of Devonshire, is that of which the diagram in page 

 256 is a compiled reduction, [a, Lowest Devonian beds of schists and red mica- 

 ceous sandstone of North Foreland ; b, red sandstone and conglomerate of Linton ; 

 c, gray schists and Stringocephalus limestone of Ilfracombe, etcetera. Beds a and 

 b are compared with the lower shelly graywacke of the Rhine (Coblenz, etcetera).] 

 It is a section across North Devon from the Foreland on the British channel, to 

 the granitic ridge of Dartmoor on the south, and exhibits a copious succession of 

 the Devonian rocks between Linton and Ilfracombe on the north, and Barnstable 

 on the south, the whole dipping under strata of the Carboniferous age, on the op- 

 posite side of a wide trough of which, or on the north flank of Dartmoor, the Upper 

 Devonian strata again rise to the surface. 



" North Devon has thus been selected as affording, on the whole, the best type 

 of succession of the rocks to which the name Devonian was applied ; because it 

 offers a clear ascending section through several thousand feet of varied strata, until 

 we reach other overlying rocks, which are undeniably the bottom beds of the true 

 Carboniferous group." 



Murchison and many later geologists, including Geikie, hold that the 

 Old Eed sandstone and the Devonian of North and South Devon are 



*See Reports of Brit. Assoc, for the Advancement of Science, 1836, Bristol meeting. Sedgwick 

 and Murchison, Trans. Geol. Soc. London, vol. v, p. 633, and Phil. Mag., vol. xi, p. 311. Lonsdale, 

 Trans. Geol. Soc. London, vol. v, p. 721. 



fSee Report on the Geology of Cornwall, Devon, and W. Somerset, by De la Beche, 1839, and the 

 Palaeozoic fossils of the same region, by Professor Phillips, 1811. 



