16 H. G. Sargent — The Penmaenmawr Intrusions. 



enstatite-diabase ; l by Zirkel as quartz-norite ; 2 and, finally, by 

 Schaub as an augite-bearing quartz-norite ! 3 



Of the two southern intrusions, tbe only mention the writer has 

 found is by Harker, 4 who refers to Carregfawr as "the smaller hill 

 half-a-mile to the south, above Tai-rhedyn". 5 



The three masses are intruded into, or perhaps have broken through 

 Lower Ordovician shales, and the accompanying Map (Fig. 1) shows 

 their surface relations to each other. It appears probable, judging 

 by penological affinities, that they owe their origin to a common 

 intercrustal reservoir. 



Scale : / in,.*= I mile. 



Fig. 1. — Sketch-map of Llanfairfechan District. Stippled areas, intrusive 

 rocks ; plain areas, Ordovician beds and Glacial Drift ; T, strike and dip 

 of cleavage. Arrows indicate direction of dip of imperfectly cleaved beds. 



On the Geological Survey Map (Sheet 78, S.E.), published in 1852, 

 the two southern outcrops are coloured as a single intrusion, the 

 area of which is extended very considerably to the south and east of 

 the limits shown on Fig. 1, so far indeed as to impinge on the lowest 

 of the lavas of Bala age. 



1 Mihr. Phys. d. mass. Gest., 2nd ed., 1887, p. 204. 



2 Lehrbuch der Petrog'raphie, 2nd ed., vol. u, p. 641, 1894. 



3 " Ueber den Quarznorit von Penmaenmawr in Wales und seine Schlieren- 

 bildungen " : Neues Jahrbuch fur Mineralogie, etc., Abh., pp. 93-121, 1905. 



4 Op. cit., p. 62. 



5 A misprint on the Geological Survey Map for Ty'n-rhedyn. 



