On the Ancient Rocks of the St. David's Promontory. 387 



In the immediate neighbourhood of St. David's they have asso- 

 ciated with them irregular bands of hard, greenish, ashy-looking 

 shales, much altered in character, but often presenting distinct 

 traces of foliation. In a ridge running from the S.E. of Ramsey 

 Sound in a north-easterly direction the greenish shales are more 

 compact, and resemble earthy greenstones. 



The quartziferous breccias and their associated shales form two 

 anticlinal axes, contiguous to each other, and have on their S.S.E. 

 and N.X.W. sides purple and green rocks. 



The order of the rocks from the quartziferous breccias upwards, 

 when not disturbed by faults, is as follows : — 



Lower Cambrian. 



1. G-reenish hornstones on the S.E., and earthy Greenstones on the N.W., 



forming the outermost portions of the so-called Syenitic and Greenstone 

 ridges. 



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



bedded in a purple matrix 60 



3. Greenish flaggy sandstones 460 



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



mains in the St. David's Promontory, namely Lingulella ferruginea 



and Leper ditia cambrensis 50 



5. Purple (sometimes greenish) sandstones 1000 



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



tonia, Conocoryphe, Microdiscus, Agnostus, Theca, and Protospongia... 150 



7. Grey, purple, and red flaggy sandstones, containing, with some of the 



above-mentioned genera, the genus Paradoxides 1500 



8. Grey flaggy beds 150 



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 these 

 rocks of the St. David's Promontory affords very important informa- 

 tion concerning the earlier forms of life of the British Isles. Until 

 the discovery of this fauna, these rocks and their equivalents in 

 North "Wales were looked upon as all but barren of fossils. We have 

 now, scattered through about 3000 feet of purple and green strata, 

 a well-marked series of fossils, such as have nowhere else been ob- 

 tained in the British Isles. In the Longmynds of Shropshire 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 regards as trilobitic, and to 

 which he has given the name of Palceopyge Ramsay i. If we assume 

 the purple and green shales and sandstones, with their associated 

 quartz rocks of Bray Head and the drab shales of Carrick M'Reily, 

 county "Wicklow, to represent the old rocks of St. David's, 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 Oldhamia. 



One very prominent feature about the palaeontology of the ancient 

 rocks of St. David's is the occurrence of four distinct species of the 

 genus Paradoxides ; and this is in strong contrast with the entire 



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