194 MR. F. R. C0WPER REED ON THE GEOLOGY OF [May 1 895, 



( n f Black shaly beds 



Lower 



,{ 



with D. Murchisoni. 



Fossiliferous ashes 

 of Saddle Point, etc. 



Felsites, tuffs, etc. 



LlTndeilo. BidymograptusMuTcMsoni-zone..^ c { rf e £f e tU p'J 5 ^ 



( Bigney, etc. 



(Black slates of 

 Tower Hill with 

 D. Murchisoni, etc. 

 Llanvien. Black slates of Blaen y Delyn with Tlacoparia, etc. 



Arenig. Slates of the district south of Fishguard. 



In conclusion I take this opportunity of expressing my thanks to 

 Mr. J. E. Marr, F.B.S., for valuable hints ; to Mr. Alfred Harker, 

 F.G.S., for some suggestions about the rocks ; to Mr. H. Keeping for 

 help in collecting ; and especially to Miss Eaisin and Prof. Lapworth, 

 F.R.S., for the loan of slides and naming of graptolites, and to Dr. H. 

 Hicks, F.K.S., for kind advice and encouragement. 



EXPLANATION OF PLATES. 



Plate V. 



Geological Sketch-map of the Fishguard-Newport district. Scale : 1 inch= 1 mile. 



Plate VI. 



Fig. 1. Perlitic felsite, showing ' crackled china ' structure and perlitic 

 cracks. The lighter portions of the slide consist of pure secondary 

 quartz ; the darker portions are cryptocrystalline. From Bwlcfa. 

 Mawr, Dinas. (Slide 316.) X68. See p. 172. 



2. Variolite with incipient varioles, skeleton felspar-crystals, etc. in 



devitrified groundmass. From Gam Fechan, Strumble Head. 

 (Slide 257.) X68. See p. 185. 



3. Porphyritic micropegmatitic groups in cryptocrystalline felsite. 



From Goodwick. (Slide 1.) x68. See p. 162. 



4. Ditto. The upper portion of this figure shows a rounded quartz- 



grain, surrounded by a later growth of micropegmatite. The lower 

 portions show well the branching radiating processes and the com- 

 posite nature of the groups. From Goodwick. (Slide 7.) X68. 

 See p. 162. 



5. Ditto. From Goodwick. (Slide 21.) x68. See p. 162. 



6. Glassy (' tachy lytic') variety of andesitic dolerite, showing groups of 



parallel crystallites of augite, globulites, felspar-crystals, etc. in the 

 devitrified groundmass. From Gam Fawr, Strumble Head. 

 (Slide 90.) X68. See p. 184. 



7. Ditto, showing skeleton felspar-crystals, and others with a granular 



core ; also feathery aggregates of felspathic fibres, groups of 

 parallel crystallites of augite, crystallites of magnetite, etc. in 

 the devitrified groundmass. From Garn Fawr, Strumble Head. 

 (Slide 101.) x68. See p. 184 and Analysis E. 



Discussion. 



Dr. Hicks congratulated the Author on having worked out with: 

 such success the geology of a very difficult tract of country. He 

 was particularly pleased to hear that the Llanvirn fauna had been 

 discovered at Fishguard, as it marked a very definite horizon, and 



