38G TEOCEEDTNGS OF THE GEOLOGICAL SOCIETY. [May 10, 



of Pembrokeshire by Mr. Hieks induced other geologists to seek for 

 similar fossils among the equivalents of these rocks in connexion with 

 the Lower Lingula-flags, which repose conformably upon the upper 

 portion of the purple rocks forming the Merionethshire anticlinal. 



In reference to the rocks which rest upon the purple strata on the 

 east side of this anticlinal, Mr. Plant communicated a memoir en- 

 titled " Notes relating to the Discovery of Primordial Fossils in the 

 Lingula-flags in the Beighbourhood of Tyddyngwladi's Silver-lead 

 Mine." An abstract of this was published in the Quart. Journal of 

 the Geol. Soc. in 1866 ; and the memoir appeared in extenso in the 

 Trans, of the Geol. Soc. of Manchester. A list of fossils obtained 

 from the Lower Lingula-flags of this portion of Merionethshire was 

 given by Mr. Plant ; and this list exhibits a series having a very 

 intimate relation with that containing the fossils obtained by Mr. 

 Hicks from Porth-y-E.haw, near St. David's. 



The Lower Lingula-flags of the valley of the Mawddach, Merio- 

 nethshu-e, are seen occurring between hard dark-grey shale-beds, 

 which aff'ord Oleni, and the highest member of the purple rocks of 

 the anticlinal ; and the Lower Lingula-flags hero are conformable 

 to the deposits above and below them. In their mineral nature they 

 have great aflinity to their equivalents near St. David's, consisting 

 of what Mr. Salter termed " sandstones probably accumulated in 

 deep water." 



The strata at Porth-y-Phaw, which are rich in Trilobitcs, contain, 

 no red or purple rocks associated with them, but are grey in colour 

 at their base, being banded by light and dark shades, and black in 

 their upper portion ; and it is in the latter that fossils are most 

 abundant. 



Beneath the grey beds, and having the same inclination as the 

 Lower Lingula-flags (Menevians) there is, in the St. David's pro- 

 montory, a great development of rocks, which exhibit red, purple, 

 green, and greenish-grey colours. These rest upon a conglomerate 

 composed of quartz pebbles, of various sizes, cemented together by a 

 reddish or purple sandy matrix. 



The beds upon which the conglomerates rest are greenish in colour, 

 and these are supported by rocks of rather peculiar characters. 



In many spots they have an aspect which so nearly resembles 

 syenite that it is, at first sight, very difiicult to make out their true 

 nature ; for they appear to be made up of crystals imbedded in a base 

 of quartz. When, however, these apparent crystals are carefully 

 examined, they are found to be, for the most part, angular frag- 

 ments of quartz, not possessing the proper crystalline form which 

 this mineral assumes. Some of the fragments have a subangular 

 outline ; and a few even manifest a distinctlj" rounded surface. The 

 matrix in which these fragments are imbedded does not exhibit a 

 crystalline arrangement, and contains a very large proportion of 

 silica as a constituent. The chemical composition of a specimen of 

 these rocks has been kindly determined by Dr. Blyth, of Queen's 

 College, Cork, and is as follows : — . 



