442 W. A. E. Ussher — PalcBozoic Boclis of Devon and Somerset. 



had been obliterated from our text-books, the general succession of 

 the rocks had been so admirably sketched by De la Beche in his 

 Eeport that, although too little quoted as an authority on the strati- 

 graphy of the subject, prevalent opinion has now endorsed the correct- 

 ness of the succession given by him ; and that succession, having been 

 endowed with a recognized nomenclature by subsequent observers, 

 now forms the basis for the discussion of a wider correlation tending 

 almost to sweep away the distinguishing epithets which had been 

 locally applied to its divisions. 



The comparison instituted by Mr, Weaver in 1839 between the 

 rocks of North Devon and the South of Ireland opened a con- 

 troversy which, after the expression of Sir R. Griffith's opinion 

 in 1842, remained tolei-ably quiescent till 1865, but has since 

 become an almost invariable element in the subsequent treatment 

 of the subject. Prof. Jukes, in 1865, 1866, 1867, and 1868, in a 

 series of papers communicated to the Roy. Geol. Soc. of Ireland and 

 the Geol. Soc. of London, reopened this controversy, maintaining, 

 in opposition to the views of previous writers, that the Lower Culm 

 Measures and Devonian rocks of North Devon were partly correlative 

 with the Carboniferous slates of the South of Ireland, partly with 

 the Old Red Sandstone. He got rid of the obstacles to his theory pre- 

 sented by the great thickness and development of the slate and grit 

 series recognized by Prof. Phillips and others as Middle and Lower 

 Devonian, by the insertion of a great East and West fault between 

 Morthoe and Wiveliscombe ; presuming that these strata, in spite of 

 strong lithological and paleeontological differences, were a repetition 

 of those on the south of the supposed fault, and regarding the 

 Pickwell Down grits as identical with those of the Foreland Group, 

 and the equivalent of the Old Red Sandstone. This view of the 

 structure of North Devon being so contrary to the then accepted 

 opinion of Prof. Sedgwick and Sir R. Murchison (who advocated a 

 conformable descending series from the Culm Measures, substituting 

 the word Devonian for Transition and Grauwacke before applied to 

 it, and regarding Devonian strata as marine equivalents of the Old 

 Red Sandstone), induced the latter to send Mr. Etheridge to Devon 

 in 1866-7, to vindicate their views. The results arrived at were 

 published in Q.J.G.S. vol. xxviii. in 1867, in the most exhaustive 

 paper that the question has elicited. In it Mr. Etheridge demonstrated 

 the accuracy of the classification put forward by Prof. Phillips in 

 1841, and endorsed. by Mr. T. M. Hall (in a lecture delivered to the 

 Exeter Naturalists' Club in 1866). He pointed out the conformity 

 of the members of the descending sequence, and the absence of any 

 great repeating fault, showing by palseontological evidence that the 

 Middle and Lower Devonian slates could not possibly be a repetition 

 of the Upper Devonian and Lower Culm Measure slates and grits. 

 Mr. Etheridge, however, admitted,^ that the Pickwell Down Series 

 may be equivalent to the Welsh and Irish Upper Old Red Sand- 

 stone. It may therefore be conceded that Prof. Jukes's papers, 

 although entirely at fault as to the stratigraphical and lithological 

 ^ Quart. Joiu'n. Geol. Soc. vol. xxviii. p. 688. 



