416 PROCEEDINGS OE THE GEOLOGICAL SOCIETY. [April 22, 



liic rocks over to the northward, after which they both dip under 

 the higher beds of Tall Petherwin and Tregiiddick Farm. 



To the eastward of the fault before mentioned, which runs down 

 to Treveny, the country opens out in the direction of the Tamer ; and 

 north of Trecarrel Bridge lower rocks rise from beneath the Lewan- 

 nick belt of volcanic ash, and form a ridge, which, commencing at 

 East Penrest, where the beds emerge from beneath the Culm-measures 

 of Cuddicombe, passes by Trebollets, PoUinny, and Trecugar to South 

 Petherwin, and is then continued by Oldwell to the north of Trevoza, 

 where these lower beds again pass beneath the Culm-measures. 

 These lower rocks consist of evenly laminated pale-green slates, 

 and are apparently unfossiliferous. As a consequence of the up- 

 heaval of the beds eastward of the Treveny fault, the continuation 

 of the higher fossiliferous slates of Tall Petherwin and Trewen, with 

 their included limestones, is carried to the northward, by Little Pe- 

 therwin and the south of Doe's Houses, to the Landlake limestone- 

 quarry, where they pass beneath the Culm-measures of Haldou 

 Down. On the other hand, we have within this semicircular ridge, 

 occupying the lower ground round about Trewarlet and Larrick, and 

 on the eastward of Lower Linnick, some of the same fossiliferous 

 slates with calcareous seams (see fig. 3). 



These upper beds are less uniform in their petrological character 

 than the pale-green slates below them. They consist chiefly of 

 olive and brownish slates, more or less rust-stained on the surface, 

 and often cleaved and splintery. Inters tratified with them are 

 thin ochreous seams, which occasionally contain fossils ; and some of 

 the olive-brown slates contain numerous minute points of ochreous 

 matter, the remains of some decomposed crystals, which give them 

 a speckled appearance. This is so frequent in the upper beds of this 

 vicinity as to be almost characteristic. The still higher slate rocks, 

 however, or those immediately beneath the Culm-measures, north of 

 Holloway Cross and Trewen, are softer and thicker, and much of 

 them is of a very pale colour and an even texture. 



The limestone at the Landlake quarry dips N.iS'.E., at an angle of 

 20°; and it is from this spot that by far the larger part of the South 

 Petherwin fossils have been obtained. The other two limestone 

 patches appear to be less highly inclined ; but there is some difficulty 

 in making out the dip satisfactorily, as the rocks are here much 

 rolled, and, moreover, they are affected by cleavage which in some 

 places is inclined in an opposite direction to the bedding, as, for in- 

 stance, in descending the hi] 1 from Little Petherwin. There appears 

 to be no reason to doubt, however, that these three small cal- 

 careous patches are on the same line of strike, curved round to the 

 northward of, and rising up to, the upraised lower rocks on the 

 south. Some of the associated slates, in fact, may be seen capping 

 the highest ground in the lane due east of South Petherwin, where 

 the included ferruginous seams contain Orthoceras ibex, Phill., a Cly- 

 menia much flattened, and some other shells ; Spirifera disjuncta 

 and Spirifera Urii occur also abundantly in some slates halfway up 

 the hill south of the Landlake quarry. In the quarry south of Doe's 



