﻿Yol. 6 I.] IGNEOUS ROCKS OF TEfE PEMBROKESHIRE COAST. 579 



28. On the Igneous Rocks occurring between St. David's Head and 

 Strumble Head (Pembrokeshire). By James Vincent Elsden, 

 B.Sc, F.G.S. (Read May 24th, 1905.) 



[Plates XXXVIII-XL.] 



Contents. 



Page 



I. Introduction 579 



II. The Contemporaneous Igneous Rocks 580 



III. The Intrusive Rocks of Strumble Head and the 



Adjoining District 581 



IV. The Intrusive Rocks of St. David's Head and the 



Adjoining District 584 



V. The Lime-Bostonite and Porphyrite-Intrusions of the 



Abercastle-Mathry District 594 



VI. Eeview of the Petrography of the Rock-types 599 



VII. Mutual Relations of the Magmas 603 



VIII. Summary and Conclusions 605 



I. Introduction. 



The area with which this paper deals adjoins the strip of coast 

 lying between St. David's Head and Strumble Head in Pembroke- 

 shire. No detailed account appears to have been given hitherto of 

 the igneous rocks of the greater part of this district, but the 

 Strumble-Head rocks have been described by Mr. F. R. Cowper 

 Reed in his paper on the geology of the Fishguard District. 1 

 Adjoining parts of the county have also received attention : 

 Mr. John Parkinson has discussed the Prescelly area, 2 and the district 

 south of St. David's, including Skomer Island, has been described 

 by various writers in considerable detail. 3 The granitic rock of 

 St. David's, of classic interest by reason of its disputed igneous 

 origin, has been the subject of exhaustive discussion by Henry 

 Hicks, 4 and has been described petrographically by Thomas Davies, 5 



E. B. Tawney, 6 Prof. Bonney, 7 Sir Archibald Geikie, 8 the Rev. J. 



F. Blake, 9 and Prof. C. Lloyd Morgan. 10 Murchison made some 

 reference to the trap-rocks of Pembrokeshire in his well-known 

 memoir, 11 and these rocks were mapped on the 1-inch scale by the 



1 Quart. Journ. Geol. Soc. vol. li (1895) p. 149. 



2 ' Igneous Rocks in North Pembrokeshire ' Quart. Journ. Geol. Soc. 

 vol. liii (1897) p. 465. 



3 See E. Eutley, ' The Felsitic Lavas of England & Wales ' Mem. Geol. Surv. 

 (1885) pp. 16, 18 ; J. J. H. Teall, ' British Petrography ' 1888, pp. 222, 284, 

 & 336 ; and F. T. Howard & E. W. Small. Rep. Brit. Assoc. 1893 (Nottingham) 

 p. 766. 



4 Quart. Journ. Geol. Soc. vol. xxxi (1875) p. 167 ; vol. xxxiii (1877) p. 229 ; 

 vol. xxxiv (1878) pp. 147, 153 ; and vol. xl (1884) p. 507. 



5 Ibid. vol. xxxiii (1877) p. 231, footnote. 



G Proc. Bristol Nat. Soc. n.s. vol. ii, pt. ii (1878) p. 112. 



7 Quart. Journ. Geol. Soc. vol. xxxiv (1878) p. 155, footnote. 



8 Ibid. vol. xxxix (1883) p. 313. 9 Ibid. vol. xl (1884) p. 302. 



10 Ibid. vol. xlvi (1890) p. 241. n 'The Silurian System ' 1839, p. 401. 



2s2 



