96 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [DeC. 2, 



tion and the cleavage cuts the beds diagonally. Sir H. T. De la 

 Beche has described the culmiferous beds as " ridged, furrowed and 

 twisted in lines, which, when not much affected by the granitic bosses, 

 have a general direction from a few degrees N. of W. to a few de- 

 grees S. of E.* ;" and the same author speaking in general terms of 

 such phaenomena says, " the lateral pressure in these older movements 

 is very considerable, so that if the multitude of contortions, domes, 

 cavities and flexures into which the beds have been forced were 

 flattened out, the area covered would be far more extensive than that 

 now occupied by the same beds in their squeezed and crumpled 

 state V This passage is peculiarly applicable to the centre of Devon- 

 shire. 



But to return to the cleavage : I traced the continuance of low 

 undulations of the cleavage, such as are described above, across a 

 band of more than five miles wide in the neighbourhood of Laun- 

 ceston from Yeolm Bridge to South Petherwin, without seeing its full 

 extent ; on the coast it reaches at least fifteen miles from Boscastle 

 to Padstow, and it may extend still farther. With so many similar 

 arches of the cleavage, it is impossible to fix upon any one line as the 

 general axis to the cleavage of the whole district, which must be as- 

 certained by drawing an arbitrary line half-way between the two 

 boundary lines of vertical cleavage. 



I can find no record of the dip of the cleavage between the cen- 

 tral portion of the district and its boundary at Bickington, nor for 

 some distance to the S. of South Petherwin. But farther southward 

 some few facts may be picked up which may be thus arranged in the 

 order of distance from the centre : near Endsleigh the cleavage dips 

 southward J ; on the Dart below Totness it dips at 4^5° to the S.§ ; 

 near Brixham, to the S.E. at a high angle |1 ; at Dartmouth the clea- 

 vage dip is southerly^; at Bigbury Bay its dip is S., but nearly 

 vertical %. 



These scanty materials make it probable that the cleavage planes 

 are arranged across these counties somewhat as in the section across 

 Carnarvonshire and Merionethshire, fig. 18, the principal differences 

 consisting in the greater diameter of the area, and in the flat undu- 

 lations of the cleavage over the centre of the district. There are 

 here also distinct proofs of the commencement of a fresh system of 

 cleavage elevation on each side of the area described. 



The comparison of the position of the cleavage planes with that of 

 the beds along the same line is interesting. Throughout the central 

 area where the cleavage is nearly horizontal, the beds undulate in a 

 succession of waves already described without offering any marked 

 features. These undulations are sharper towards Bideford, where we 

 may expect to find the cleavage highly inclined**. At the Bicking- 



* Report on Cornwall, &c., p. 124. 



t Memoirs of the Geological Survey of Great Britain, vol. i. p. 222. 



X De la Beche, Report on Cornwall, &c., p. 108. 



§ Sedgwick and Murchison, p. 655. 



II De la Beche, Report on Cornwall, &c., p. 45. % Ibid. p. 77. 

 ** See wood-cut at p. 123 of Sir H. T. De la Beche's Report. 



