688 Professor Sedgwick and R. I. Murchison, Esq., on the 



On the Physical Structure of Devonshire, and on the Subdivisions and 

 Geological Relations of its older stratified Deposits, &;c. 



[Read April 24th, 1839.] 



PART II. 



On the Classification of the older stratified Rocks of Devonshire and 

 Cornwall, Sfc. 



In a former communication we described the mineral structure, and the 

 order of superposition, of the successive groups of rocks which are crossed 

 by a section from the north, to the south coast of Devonshire ; and by 

 following the beds (along their line of strike) into Cornwall, we were 

 enabled, within certain limits, to bring the killas (or slate rocks of that 

 county) into comparison with some of the lower Devonian groups. In this 

 way, we ascertained the existence of a great culmiferous trough, superior 

 to all the other groups in North Devon, and distinguished from them both 

 by its physical structure and its organic remains. Hence we concluded, that 

 the culmiferous series must be represented, for the future, in our geological 

 maps by a distinct and appropriate colour. We had stated the same conclusion, 

 and on precisely the same evidence, at the meeting of the British Association 

 in 1836. We further concluded, that, at least, all the upper portion of this 

 series was of the age of the great coal-formations of England ; inasmuch as 

 all its vegetable fossils, as far as they were ascertained, agreed specifically 

 with undoubted coal plants. To this conclusion we still adhere ; and we re- 

 gard the culmiferous rocks as forming a true geological horizon, to which 

 either the ascending or descending series of deposits may be referred. 



Again, in the arrangement of the several groups below the culm-trough, 

 as they appear on the North Devon section, we have no modifications to 

 suggest; and the very illustrations which were before suspended (1837), 

 to explain the actual succession of the deposits, will serve our purpose at 

 this moment. 



Since our first notice of this section in 1836, Mr. De la Beche has exa- 

 mined the country in great detail; and his arrangement of the several fossil- 

 iferous groups, inferior to the lower culm beds, agrees with our own *. The 



* There is one unimportant exception to this remark which we have noticed in our former paper 

 (see p. 642, note). It fortunately does not affect the position of the fossiliferous groups, or any 

 question connected with their classification. 



