Vol. 55.] GEOLOGY OF NORTHERN ANGLESEY. 639 



includes them in his ' Disturbed Volcanic Group,' and claims the 

 fossils as pre-Cambrian (Monian)/ As I have found abundant 

 examples of Ortliis caUigramma in these beds, they are un- 

 doubtedly Ordovician ; but the determination of their age does not 

 carry that of the Green Series with it. 



8ir A. Geikie mentions ■ a fossiliferous limestone near Carmel 

 Head as proving the Bala age of the green beds ; but it is worthy 

 of note that, though Ramsay recorded that ' a few poor fossils ' ^ 

 indicated a Bala age, his map shows that he was satisfied that the 

 fossil-bearing bed was distinct from the Green Series. I have 

 collected fossils from this limestone ; but, as the relationship of this 

 bed to the Ordovician and the Green Series is rather a question of 

 stratigraphy, this point will be taken up again in dealing with the 

 stratigraphical evidence. 



We will now compare the fossils that occur in the rocks north 

 of the barren Green Series with those that are found south of 

 that series, as this should throw some light on the succession. For, 

 if we consider the green rocks to be conformably interbedded 

 between the Ordovician on the south and the fossiliferous beds on 

 the north, we assume a general ascending succession from south 

 to north, and we therefore ought to expect that fossils found along 

 the northern coast will belong to a higher zone than any horizon 

 occurring in the southern rocks. 



(i) Fossils north of the Green Series. 



Fossils have been known to occur at three localities in Northern 

 Anglesey, namely : — the tramway at Craig V^en, already mentioned ; 

 Forth Padrig, near Cemaes ; and in a limestone at another Forth 

 Fadrig, north-west of Mynachdy ; but Ortliis Bailyana is the only 

 fossil hitherto identified. I have succeeded in finding identifiable 

 specimens in several localities, and append a list. 



(a) Forth Fadrig. Black Shales. — Most of the forms have 

 been sheared out of recognition, but I have collected the following 

 graptolites : — 



Didymograptus superstes, Lapw. j Coenograptus gracilis, Hall. 



Dicellograptus sextans, Hall. Leptograptus sp. 



Ciimacograptus ScJiarenbergi, Lapw. Dicranograptus sp. 



Diplograptus euglyphus, Lapw. 



(jG) In the same beds, in the Vicarage grounds above the Forth, 

 I obtained : — 



Fatenda balcletcliiensis, Dav. I Siphcmotreta (?). 



Acrotreta sp. I 



^ Quart. Journ. Geol. Soc. vol. xliv (1888) pp. 523 & 542 ; G-eol. Mag. 1890, 

 p. 312. [This statement requires some modification, as Frof. Blake pointed out 

 in the discussion, and I willingly' make the desired correction. In his paper 

 of 1888 he regarded the Monian age of these beds as only ' probable,' stating at 

 the same time that he was 'quite ready, if possible, to receive the fossils as 

 characteristic' of his Monian system.] 



2 Pres. Addr. Quart. Journ. Geol. Soc. vol, xlvii (1891) Proc. p. 132. 



■' Mem. Geol. Surv. 'Geol. N. Wales,' 2nd ed. (1881) p. 229. 



