18 H. G. Sargent — The Penmaenmawr Intrusions. 



a resisting obstacle ; and (2) that the intrusion is consequently older 

 than the cleavage. The beds on the south of the intrusion could 

 more easily yield to a pressure coming from the direction suggested, 

 and the cleavage there would thus be less perfect. The general 

 direction of the axes of disturbance that produced the cleavage over 

 the Carnarvonshire area was S.E. to N.W., as shown by Mr. Harker. 1 

 Near Dinas and Carregfawr the exposures are too few and too poor 

 to form satisfactory conclusions as to the relations of the slates to the 

 igneous rock, though here too a similar parallelism seems to be at 

 times approached. 



Assuming, on the authority of Ramsay, 2 that the cleavage was 

 effected "before the commencement of the deposition of the Upper 

 Llandovery strata", it seems probable that these intrusions were 

 contemporaneous with the great manifestations of igneous activity in 

 Carnarvonshire, which are recognized to be of Bala age. Schaub, 3 



Fig. 2. — Sketch-map of Penmaenmawr. 



without adducing evidence, states that Penmaenmawr is younger than 

 Silurian and of late Palaeozoic age. In the absence of evidence it is 

 impossible to examine the reasons for this view. 



The extensive quarrying operations on Penmaenmawr facilitate 

 examination of the rock from the margin to the centre of the mass, 

 and three distinct varieties grading into each other may be observed — 

 (1) the marginal rock, dark-coloured, very compact, and at times 

 somewhat cherty in appearance ; this merges into (2) a fine-grained 

 variety, rather lighter in colour, often of a bluish and sometimes of 



1 The Bala Volcanic Series of Caernarvonshire, 1889, p. 113. 



2 The Geology of North Wales (Mem. Geol. Surv. England and Wales), 

 vol. iii, 2nd ed., p. 326, 1881. See also Harker, "Notes on the Geology of 

 Mynydd Mawr" : Geol. Mag., Dec. Ill, Vol. V, pp. 221-6, 1888. 



3 Op. cit., p. 94. 



