Tlte Occurrence of Pre -Cambrian Shale in Guernsey. 469 



to observers of the Jersey sedimentaries and of the " Phyllades de 

 St. L6 " in Normandy. 



While examining this small area in the spring of 1920, with a view- 

 to correlation with the Jersey sedimentary beds, the present writer 

 discovered another outcrop near by, which had hitherto escaped 

 the notice of earlier investigators. It was re-examined in April 

 of this year. 



The section is a roadside exposure on the Torteval Road, 75 yards 

 'to the eastward of Westend Cottage (2 in. Ordnance Survey Sheet 

 of Guernsey). 



Westend Cottage is about 2,500 yards S.S.E. of Fort Pezerie, and 

 1,500 yards due east of Pleinmont Point. 



The exposure is 37 yards in extent along the road, showing a height 

 above road level of at most 3 feet. A turf wall, 4 feet in height, has 

 been constructed above it. Outcrop occurs only on the south side 

 of the road. 



The rock is a fine mudstone, showing the distinctive appearance, 

 colouring, bedding, and fracture, of the Jersey shales. A green 

 satin-like surface is developed on the bedding-planes, as at St. Lo. 

 Eastward, the beds cease by intrusion of a gneissic rock, which may 

 be tentatively described as of dioritic origin. 



At the point of igneous intrusion the beds dip to the north at an 

 angle of 10 degrees. This condition persists for 5 feet westward. 

 For 7 yards, still to west, the shales are broken and crushed, having 

 no recognizable or reliable dip. A further 4 yards westward shows 

 a high dip to the east. The remaining 24 yards exhibit a dip of 

 10 degrees to the north. There is suggestion of shear through the 

 middle of the section. The exposure occurs along an east-west 

 direction, at an altitude of 210 feet. To the south is nothing but 

 dioritic gneiss, with inadequate evidence of relationship. If the 

 beds continued according to their northward dip, they would reach 

 sea-level about 1,400 yards to the north, thus providing a strike 

 running through the Fort Pezerie area. 



Faulting in an east-west direction, rather common in this part of 

 Guernsey, has apparently preserved these small areas by down- 

 throw ; a north-south faulting, a very noticeable feature in the 

 south of Guernsey, has restricted the outcrop. 



The fact noted by Professor Bonney that " diabase " invades 

 both sedimentary beds and the gneiss, and that all three are invaded 

 by a " red " dyke (the pre-Cambrian aplite, common in all of the 

 Channel Islands), appears to establish the pre-Cambrian age of these 

 beds. 



