676 PEOF. W. W. WATTS ON THE MICKOSCOPIC STUDY [Aug. 1 899, 



little but sericite. More usually the groundmass is made up of 

 fine chlorite-flakes embedded in granulitic quartz. Epidote in 'veins 

 and isolated crystals is usually present. Secondary cbalcedonic 

 silica has often been deposited along planes and lenticles pro- 

 duced by the movement. In the finer-grained rocks strain-slip is 

 present, and not infrequently the rock is brecciated and contains 

 fragments derived from itself; one example (N.A. 43, from the 

 Craig Wen ' quartz-knob ') has the structure of a mylonite. One 

 rock (jS^.A. 18, near Taldrws, Cemlyn) has been detected in the 

 Green Series which contains, in addition to angular grains of quartz, 

 several fragments of orthophyre, of angular grit, and crushed rock. 

 Another rock (N.A. 70, Hell's Mouth) in this series contains frag- 

 ments, possibly of volcanic origin. The rock from Forth yr Ysgraff 

 (N.A. 20), found in the neighbourhood of a dyke and of serpentine, 

 exhibits dark spots, probably developed by contact-action subse- 

 quently to foliation. A specimen of Llanfechell Grit (N.A. 86, 

 Pen-y-bont) contains fragments of granulite, quartz-schists, micro- 

 pegmatite, and felspar, all clearly derived from an area of foliated 

 rocks. The bulk of the rocks may be spoken of as chloritic 

 schists, chloritic and sericitic phyllites, and phyllitic 

 grits. 



(2) The Ordovician Rocks. 



The rocks examined are mostly from the neighbourhood of the 

 junction with the Green Series, collected with the view of obtaining 

 evidence from the contained fragments, or else from the Ordovician 

 beds in the Northern Complex. A typical specimen (N.A. 53, 

 from Cefn-du-mawr, Llanfair-y'ughornwy) contains, among abun- 

 dant angular fragments of quartz, granulated and non-granulated, 

 the following larger fragments of rocks: — {a) sericitic phyllites 

 consisting mainly of granular quartz with little sericite ; (6) well- 

 foliated sericitic phyllites with minute quartz-grains; (c) sericitic 

 phyllites with larger quartz- grains; (d) fine sericitic ph541ites con- 

 sisting almost solely of sericite ; (g) green quartz-chlorite-schists ; 

 and (/) fine gritty rocks. All these types have been found among 

 the rocks of the Green Series examined, and all are in precisely the 

 same stage of metamorphism as in the fragments. Other examples 

 of the rocks contain fragments of quartzose grits, quartzites, and 

 rocks quite un distinguishable from those of the ' quartz-knobs.' In 

 one specimen there are abundant fragments of a limestone now 

 crystalline. No volcanic fragments have been discovered in any of 

 the specimens examined by me, with the exception of one doubtful 

 instance from the western Perth Padrig, In a few cases, where 

 there has been much movement, the groundmass of these rocks, 

 and of the finer bands within them, becomes a sericitic schist. 

 The state of metamorphism of the rock-fragments indicates that 

 there must be a considerable gap between the Ordovician rocks 

 and those of the Green Series. The rocks from Mynydd-y-Garn 

 (N.A. 74 & 75) contain fragments of granitic, gneissic, and schistose 



