1871.] HAEKNESS ANB HICKS — ST. DAVId's PROMOl^TOEY. 391 



Sound, these grey fossiliferous grits are not seen : a fault having 

 an E.N.E. course has cut through the upper portion of the purple- 

 coloured rocks which support the grey sti-ata, A few heds of these 

 grey grits, however, are seen on the JST.N.W. side of this fault, near 

 Ogaf Golhfa, in Whitesand Bay, reposing upon the higher members 

 of the purple flags and sandstoaes. The order of the rocks from the 

 quartziferous breccias upwards, when not disturbed by faults, is as 

 follows : — 



Lower Cambrian. 



feet. 



1. Greenish hornstones on the S.E., and earthy greenstones on the N.W., 



forming the outei-most portions of the so-called Sjenitic and Green- 

 stone ridges. 



2. Conglomerates composed chiefly of well-rounded masses of quartz im- 



bedded in a purple matrix 60 



.3. Greenish flaggy sandstones 4G0 



4. Eed flaggy or shaly beds, affording the earliest traces of organic re- 



mains in the St. David's Promontory — namely, lAngidella ferritginea, 

 Leper ditia cambrensis, a larger Lingulella, and a Discin a 50 



5. Purple (sometimes greenish) sandstones 1000 



6. Yellowish-grey sandstones, shales, and flags containing the genera 



Phdonia, Conocoryphe, MicrodUcus, Agnostus, Theca, Protospongia, 



and Paradoccides 150 



7. Grey, purple, and red flaggy sandstones, containing most of the above- 



mentioned genera 1500 



8. Grey flaggy beds, containing Paradoxides aurora 1 50 



9. The true beds of the "Menevian Group," richly fossiliferous, and the 



probable equivalents of the lowest portions of the Primordial Zone 



of M. Barrande 550 



The discovery of a fauna specially rich in Trilobites among the 

 purple and green rocks and their associated strata of the St. David's 

 promontory affords very important information concerning the earlier 

 forms of life which occur in the old sedimentary deposits of the British 

 Isles. Until the discovery of this fauna, these rocks and their equi- 

 valents in North Wales have been looked upon as all but barren in 

 fossils. We have now scattered through about 3000 feet of purple 

 and green strata a ivell-marlced series of fossils such as have nowhere 

 else been obtained in the British Isles. 



In the Longmynds of Shropshire, consisting of purple and green 

 rocks, which probably represent the rocks having the same colour 

 in the St. David's district, the only evidence of the existence of 

 life during the period of their deposition is in the form of worm- 

 burrows — and in the somewhat indistinct impressions which Mr. 

 Salter regarded as trilobitic, and to which he has given the name 

 PcdcBOiDyge Ramsayi *. 



If we assume the purple and green shales and sandstones with 

 their associated quartz rocks of Bray Head, and the drab shales of 

 Carrick McReily, co. Wicklow, to represent the old rocks of the St. 

 David's promontory, they afford only very meagre evidence of the 

 occurrence of life during the period of their deposition, in the form 

 of worm-burrows and tracks and in the very indeterminate fossils 

 which have been referred to the genus Olclhamia. 



■* Quart. Journ. Geol. Soc. vol. xii. p. 2-19. 



