Mineralogy and Geology. . 113 



In Devonshire he establishes two lines of vertical cleavage, sixty- 

 miles apart, one at Stoke Fleming the other at Bickington ; and they 

 hound a broad area over which the cleavage planes undulate in low 

 flat waves, the axes of which bear Firr. 11. 



between E. and E.N.E. The an-> ^ ^p^ 



nexed cut represents the relation of ^?^^^— mSm 



the planes of bedding and cleavage 

 in these undulations near Launces- 

 tovvn and on the coast near Tintagel. The continuous lines represent 

 the bedding and the dotted lines the cleavage. After staling other sim- 

 ilar facts from different districts in England, Mr. Sbarpe remarks as 

 follows, with regard to the relation of the cleavage planes to the bed- 

 ding in Devonshire : 



" 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 v 



this] „ „, „„,..„...,„-, 



cleavage. From Pilton to llfracombe. with cleavage highly inclined, the strata 

 are elevated in higli hills, and at Linton, where the inclination of the cleavage is 

 only 35°, the bed? seldom dip more than 5°. So again on the S. const of Devon- 

 shire, disturbed and elevated strata occur in company With highly inclined cleav- 

 age. These observations arc less complete than those relating to Carnarvonshire, 

 but the theoretical conclusions to be derived from them are the same. 



"The regularity of the direction of the cleavage is not at all broken in the neigh- 

 borhood of the granite of these counties, from which it is to be inferred that the 

 granitic eruptions had taken place and become solid before the cleavage was pro- 

 duced : indeed some remarks of Sir H. T. De la Beclie lead me to suppose that 

 thecleavage is continued through the granite." 



Mr. Sharps having deduced from the distorted shells thai " the slaty- 

 rocks had undergone compression in a direction perpendicular to the 

 pi ies of cleavage," and " that this compression was compensated by 

 an expansion in the direction of the dip of lUe cleavage," enters upon 

 an explanation of the non-conformity of the bedding to the cleavage 

 planes. Assuming that the elevation was produced by an elevating 

 force beneath the area, he argues that there will result from such ele- 

 vating action, besides a grand central arch or anticlinal axis, other sub- 

 ordinate fractures and dislocations either side ; and that thus the vartous 

 anticlinal axes in figure 9 were produced, while only the mam or cen- 

 tal one influenced the direction of the cleavage planes. VV itb regard 

 to the manner in which the cleavage structure has been ^™%™ 

 because of this peculiar feature, Mr. Sharpe s.mply e ^ * n^me 

 °f the views which have been presented, expressing at £"»*™ 

 l »e hope that the observations he has made may hasten f*™™*?^ 



— ..up C mat. me oDservauous ue iwa m««« ■ — j . . t 



a " end which must surely be promoted by obse. vat.ons o so g re 

 *rest followed out with the care and discriminate exhibi ted nr me 

 Portant memoir, of which a brief abstract has been here ore* tme . 



4 Geological Society of London, ^^}™^V**\ F icld 

 *ad, entitled, "On the Structure and probable Age ol t >e 

 °J the James river, near Richmond, Virginia;" by Charles Watt, 

 F -RS., V.P.G.S. 



Swosd Sek.ks, Vol. IV. Ho. lO.-July, W- U 



