THE 



LONDON AND EDINBURGH 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[THIRD SERIES.] 



APRIL 1839. 



XL. Classification of' the Older Stratified Rocks of Devonshire 

 and Cornwall. By the Rev. Professor Sedgwick, F.R.S. 

 F.GS., and Roderick Impey Murchison, Esq., F.R.S. 

 F.G.S.* 



IT was the general belief of geologists, when we commenced 

 * our examination of Devonshire, in the summer of 1836, 

 that the larger portion of its area was occupied by greywacke 

 or transition rocks of high antiquity, from which the culm- 

 bearing stiata of Bideford, and many other places in the 

 county, could not be separated. Having occupied ourselves 

 for some years in deciphering the relative age of the older 

 rocks of England and Wales, we were naturally anxious to 

 apply to this county those principles of classification by which 

 the successive subdivisions of the Silurian, and (though much 

 more imperfectly) also of the Cambrian System, had been de- 

 termined ; for it seemed to us very anomalous, that the culm 

 beds of Devonshire, though stated to resemble those of the 

 coal field of Pembrokeshire, both in their mineral characters 

 and in their associated fossil plants, should be interpolated 

 among the most ancient greywacke rocks of the county. Mr. 

 De la Beche had, however, in a communication to the Geo- 

 logical Society, stated that such was their position ; and he 

 completed an Ordnance geological map, in which all the culm 

 rocks, as well as all the so called greywacke rocks of Devon, 

 were represented under one uniform colour. This map we 

 purchased many months before we commenced our examina- 

 tion of Devonshire. An outline of tlie results of this exa- 

 mination was laid before the British Association in the autumn 

 of the same year; and we exhibited a section from the north 

 coast to Dartmoor, (copied, though not (juite correctly, in the 

 * Coinmiiiiicatcd by the Authors. 

 Phil. Mag. S. J. Vol. it. No. 60. April 1839. R 



