Vol. 51.] GEOLOGY OF THE COUNTRf AROUND EISHGUAED. 149 



16. The Geology of the Country around Fishguard, Pembroke- 

 shire. By E. E. Cowper Eeed, Esq., M.A., E.G.S. (Read 

 January 28rd, 1895.) 



[Plates V. & VI.] 



Contents. 



Page 



I. Introduction , 149 



II. Structure of the District 150 



III. Folds, Faults, etc 151 



IV. Relation of the Form of the Ground to the Geo- 

 logical Structure 152 



V. Stratigraphy and Petrography : 



(a) The Sedimentary Rocks 153 



(b) The Contemporaneous Volcanic Rocks : 



(1) General Characters and Distribution ... 158 



(2) Microscopic Characters of the Lavas ... 16 L 



(c) The Pyroclastic Rocks 175 



(d) Chemical Composition of the Volcanic Rocks . 177 



(e) The Intrusive Rocks : 



(1) Distribution and Structure 179 



(2) The Crystalline Intrusive Rocks and their 



Mineralogical Composition 180 



(3) The Variolitic and other Varieties of the 



Intrusive Rocks 183 



(4) Specific Gravity of the Intrusive Rocks . 191 



(5) Chemical Composition and Age 192 



VI. Correlation with other Areas 193 



I. Introduction. 



On the northern coast of Pembrokeshire there lies a district of con- 

 siderable area which has not been geologically investigated since 

 the completion of the Government Survey under De la Beche in 

 South Wales. The region adjoining that to be described in this 

 paper has been made known to us in detail by the labours of 

 Dr. Henry Hicks and others during the last few decades ; and we 

 may therefore claim a fairly complete acquaintance with the 

 Archaean, Cambrian, and Ordovician rocks of South-west Pembroke- 

 shire. North-east of a line running from Penclegyr Point on the 

 coast inland to St. Elvis in the south, we have had, however, to 

 confess comparative ignorance. 1 The Geological Survey memoir on 

 South Wales pays scant attention to this district, and relatively 

 little information of importance can be obtained from any subse- 

 quent geological literature. 



My object in visiting this tract of country was to determine the 

 age of the volcanic series indicated on the Survey map near the 



1 Murchison mentions the 'trap rocks' near Fishguard in his 'Silurian 

 System' (1839), pt. ii. p. 401 ; and De la Beche in a note to his ' Geology of 

 Southern Pembrokeshire,' Trans. Geol. Soc. ser. 2, vol. ii. pt. i. (1826) p. 3. 



