638 MR. C. A. MATLEr ON THE [Aug. 1 899, 



my microscopic slides have yielded very little evidence of this, I 

 have found a rock containing some volcanic fragments in the series 

 near Taldrws, Cemlyn. The detailed stratigraphy of this Green 

 Series is very complicated, and requires working out ; but the succes- 

 sion may be provisionally stated as below, in descending order : — 



(1) Cemlyn Flaggy Grits, Phyllites, and Shales. 



(=:Llaneilian Beds in part.) 

 . (2) Rhosbeirio and Cemaes Shales and Slates, with Grit-bands. 



( = Llaneilian Gnarled Series in part.) 

 (3) Llanfechell Grit and Mynydd Mechell Chloritic Schists. 



Numerous dykes and bosses cut through these beds. Some are 

 acid, others basic, and ophicalcites and serpentines also occur. Their 

 relationships are interesting, but do not come within the scope of 

 this paper. 



(b) The Northern Complex. 



This group of rocks lies along the coast, north of a line running 

 almost due east-and-west from Mynydd Wylfa to Bull Bay, passing 

 a little north of Cemaes Pier. Among these rocks are some that 

 correspond with the Green Series farther south, but the bulk have a 

 very diiferent facies. Prof. Blake says that this part of the district 

 may be roughly described as ' full of agglomerates, coarse ashes, 

 quartz-knobs, limestones, and conglomerates.'^ As some of these 

 rocks owe their clastic appearance to crushing, their description 

 may be more fitly left till the effects of earth-movements have been 

 considered. 



(c) The Ordovician Rocks. 



These lie in the jSTorthern Complex in strips and patches. They 

 consist of conglomerates and pebbly sandstones, grey sandy shales, 

 and black argillaceous shales with some ironstone. As they are 

 found associated with the last-mentioned group, their fuller con- 

 sideration will be also deferred to a later part of this paper. 



IIT. Relation op the Green Series to the Ordovician. 



The arguments for and against the Ordovician age of the Green 

 Series fall under two heads — palaeontological and stratigraphical. 



(a) Palseontological Evidence. 



The Ordovician age of the Green Series has been inferred, 

 on palaeontological grounds, from certain fossils mentioned as 

 occurring near Craig Wen and in a limestone near Carmel 

 Head. Prof. Hughes discovered Orthis Bailyana and other Orthides 

 in the beds cut through by the tramway at Craig Wen. These 

 beds are not, however, part of the Green Series ; Prof. Blake 



1 Quart. Journ. Gaol. See vol. xliv (1888) p. 517. 



