262 



ME. W. G. SHA^yOX OX A 



[vol. Ixxviii, 



II. Field Eelatioxs. 





CO 



O 



§5 





The summit of Knowles Hill has been quarried, and a smaller 



quany exists by the footpath on the 

 north of the hill, bordering the Teign 

 alluvium. The rocks described are 

 mainly from the upper quarry. The 

 northern slopes of the hill are in 

 pastm-e, and the exposm-es are too 

 Aveathered to admit of a peti'ographic 

 description of the rocks ; on the east, 

 the geological lines have been drawn 

 from very limited exposures, as the 

 area has been completely built over. 

 The sill is intrusive into Upper 

 Devonian slates ; its lower boundary 

 is indicated by the fact that the floor 

 of the quarry is in slates, the whole 

 of the sill having been quamed away. 

 The upper limit is indicated by the 

 occurrence of spotted slates, the 

 alteration extending for a distance of 

 6 to 9 inches from the contact ; this 

 clearly shows the intrusive natm'e of 

 the dolerite. The total thickness 

 estimated from these facts gives, at 

 the southern wall of the quarry, only 

 15 feet ; within a distance of 30 

 yards this has expanded to 30 feet, 

 ^'.'.^ j^ 3 and the top is not seen, the sill on 

 the north-eastern face becoming more 

 laccolitic in habit. The notable 

 differentiation occurs in the narrow 

 portion. A thin cover of slates 

 separates this upper quarry from a 

 w \:"\\N^ '-' 2 ^ small outcrop on the south-east, and 



at the edge of the same field on the 

 south- south-west picrite is visible 

 beneath a thin cover of slates. It is 

 probable that the top of the quarry 

 is very little below the upper limit of 

 the sill. 



Some evidence can be obtained for 

 the existence of small thrust-planes 

 or slig-ht faultino- : — 



> 









(i) The slates on the floor of the quarry 

 are not spotted. 



(ii) The slates on the south-west of the 

 quarry abruptly change from purple to black, and are accompanied by a more 

 compact rock ivhich appears to have been a tuff, but has also undergone 



