1922.] GEOLOGICAL NOTES. ( J/ 



The section is a roadside exposure on the Torteval Road, 

 75 yards to the eastward of Westend Cottage (2m. 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 Plemmont Point. 



The exposure is 37 yards in extent along the road, show- 

 ing 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 bed- 

 ding-planes, as at St. L6. Eastward, the beds cease by in- 

 trusion 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 clip of 10 degrees to the 

 north. There is suggestion of shear through the middle of 

 the section. The exposure occurs along an east-west direc- 

 tion, 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 clown-throw; a north-south faulting, a very notice- 

 able feature in the south of Guernsey has restricted the out- 

 crop. 



The fact noted by Professor Bonney that " diabase " 

 invades both sedimentary beds and the gneiss, and that all 

 three are invaded by a il red " dyke (the pre-Cambrian aplite, 

 common in all of the Channel Islands), appears to establish 

 the pre-Cambrian age of these beds. 



[Reprinted by permission from the Geological Magazine , 

 Vol. LIX. pp. 468-9, October, 1922.] 



