Vol. 68.'] PEE-CAMBEIAN AND CAMBRIAN OF PEMBEOKESHIEE, 377 



{b) Bibliography, 



<1) MuRCHisoN, Sir Eoderick, ' Silurian System ' 1839, pp. 374, 379. 



(2) E-AMSAY, Sir Andrew. — Report on the St. Davids & adjoining district, 



circa 1842, preserved at the office of the Geological Survey. 



(3) One-Inch Map, Sheet 40, Old Series, 1st edit, published by H.M. Geo- 



logical Survey, 1845. 



(4) Sheet 1, Horizontal Sections, 1st edit,, published by H.M. Geological 



Survey, 1845, 

 •<5) De la Beciie, Sir Henry,— Mem. Geol, Surv. vol. i (1846) pp. 229, 230. 



(6) AvELiNE, W. T. — ' MS. Notes on the St. David's & adjoining district, made 



during the revision in 1855 of Sheet 40 of the map, preparatory to the 

 last edition (see below).' Preserved in the office of H.M. Geological 

 Survey, and dated 1855. 



(7) One-Inch Map, Sheet 40, Old Series, last edition, published by H.M. 



Geological Survey, 1857. 



(8) Sheet 1, Horizontal Sections, last edition, published by H.M. Geological 



Survey, 1857. 



(9) Hicks, H, — 'Additional Notes on the Dimetian & Pebidian Eocks of 



Pembrokeshire, witli an Appendix bv T. Davies ' Quart. Journ. Geol. 

 Soc, vol. xxxiv (1878) p. 153. 



(10) Hicks, H. — ' On a New Group of Pre-Cambrian Eocks (the Arvonian) in 



Pembrokeshire, with an Appendix by T. Davies ' Quart. Journ. Geol. 

 Soc. vol. XXXV (1879) p. 285. 



(11) Hicks, H, — 'The Classification of the Eozoic & Lower Palgeozoic Eocks 



of the British Isles' Pop. Sci. Eeview, n. s. vol. v (1881) p. 295. 

 {12) Geikib, Sir Archibald. — ' On the Supposed Pre-Cambrian Eocks of 

 St. David's ' Quart. Journ Geol. Soc. vol. xxxix (1883) p. 261. 



(13) Blake, J. F.— 'On the Volcanic Group of St. David's' Quart. Journ. 



Geol. Soc. vol. xl (1884) p. 294. 



(14) Hicks, H. — ' On the Pre-Cambrian Eocks of Pembrokeshire, with especial 



reference to the St. David's District ' Quart. Journ. Geol. Soc. vol. xl 

 (1884) p. 505. 



(15) Hicks, H. — 'The Pre-Cambrian Age of certain Granitoid, Felsitic, & 



other Eocks in North- West Pembrokeshire ' Quart. Journ. Geol. Soc. 

 vol. xlii (1886) p. 351. 



(16) Thomas, H. H., in the Summary of Progress of the Geological Survey for 



1908, Mem. Geol. Surv. 1909, p. 30. 



(17) Green, J. F. N., in Proc. Geol. Assoc, vol. xxii (1911) p. 215. 



II. The Pee-Cambkian Rocks. 



The pre-Cambrian rocks of this district, as at St. David's, may 

 be separated iiito two main divisions : — an older division consisting 

 largely of fragmental and extrusive rocks, and a younger division of 

 which the rocks are essentially intrusive. For these two groups we 

 retain the respective names Pebidian and Dimetian, which 

 were applied by Henry Hicks to similar rocks in the district of 

 St. David's, and also suggested for some of the rocks within the 

 district under description. 



{a) The Pebidian. 



Eocks of this division make up a large proportion of the area 

 occupied by the pre-Cambrian formations ; but, although various 

 types can easily be distinguished in different parts of the district, 

 no detailed subdivision of the rocks classed by ns as Pebidian was 

 attempted. 



2e2 



