1868.] IIOLL — SOUTH DKVON AND EAST CORNWALL. 4013 



remains. These beds rise gently towards the south ; but the chert 

 is much contorted. Yellowish or greenish Culm-measure sandstones, 

 with j)lant-remains, are also seen in a small roadside excavation 

 half a mile to the south-east of Hardow Down, opposite the turn-off 

 to Burdown, dipping S. 40° E. From this place the line of junction 

 between the two formations passes in a southerly direction to near 

 St. Lavers ; but a small outstanding patch of chert occurs in a field a 

 little south-east of Trewarlet, resting upon slates which contain fos- 

 siliferous seams, w^hich appear to be on the horizon of the Pether- 

 win beds. These slates dip due south, while the chert in the field dips 

 south-west at a low angle, and is underlain by thin grey grit exposed 

 near the entrance to tlie field. Bej'ond the slates, and about half- 

 way between the chert-quarry and St. Lavers, the lane is crossed by 

 a fault running N.E. and S.W., which brings down a narrow strip 

 of Culm-measure slate and grit, together with some calcareous vol- 

 canic ash, dipping S.W. On the south side of the little stream, how- 

 ever, we almost immediately come to pale-green slates belonging to 

 the underlpng series, dipping S. 20° E, at a rather high angle ; and 

 this dip is continued to beyond Lezant. 



From St. Lavers the line passes south of Landue MiU, and across 

 the Callington turnpike-road, in a south-easterly direction, at a spot 

 where unconformability is noticed by Sir Henry De la Beche* (but 

 which in reality is a line of fault, as his sketch clearly shows), and 

 thence on towards Lowley Bridge. Before reaching Cudducombe, 

 however, we again find Culm-measure slates and grits, the line be- 

 tween them and the underlying rocks recrossing the turnpike-road 

 to Trekenna, whence a long narrow strip of Carbonaceous rocks runs 

 along the northern slope of the ridge which extends from East Pen- 

 rest to beyond TreboUets. Along this narrow strip the chert, which is 

 well exposed in the quarries opened for road-stone, is for the most part 

 white, and dips north-east ; but the bedding is much contorted, and 

 southerly dips occur lower down in the valley. On the high ground 

 south-east of Lazant, near a place marked " Buins" on the Ordnance 

 Map, coarse thick slates are exposed in a roadside-cutting; but I could 

 not satisfy myself whether they belonged to the Culm-measures or to 

 the underlying series. 



Descending the hill from Cudducombe to the Inny river, either by 

 the CaUington turnpike-road or by the lane which leads to Trehing- 

 stow, we pass over dark-coloured slates with thin grey grits dipping 

 S. 20° W. These beds cross the river below Trecarrel Bridge, and 

 are separated from the volcanic ash on the south side of the stream 

 by a very inconsiderable thickness of the lower slates, as seen in the 

 section on the road from the bridge to Linkinghorn ; but unfortunately 

 the actual contact is obscured by rubble. At Tregvis the beds dip 

 S. 20° E., but halfway thence to Lower Trelabe they dip N. 25° E. 

 at 5°. Between these two places occurs the axis of a synclinal 

 trough occupied by Culm-measures, which here consist chiefly of 

 slates, often of dark colour, and thin grey grits, with one or two in- 

 considerable bands of volcanic ash near Congdon. These beds run 

 '•^ Eep. p. 107, and woodcut. 



