34 Revietvs — The Palceontographical Society. 



Sheet No. 1. — The outermost bed is well seen in the quarries at 

 Coed-y-Glyn, on the west side of the valley, and in a small cutting 

 on the hillside on the east side. It is 45 feet thick on the level of 

 the road, but thins out rapidly to the north, as at a short distance 

 away it only measures 28 feet. Baked slates lie in contact on both 

 its upper and lower surfaces. 



The rock consists of a felted aggregate of felspar microliths, and is 

 aphauitic in texture. The upper margin for 5 feet and the lower 

 part for 2 feet are amygdaloidal. Near the upper surface the micro- 

 scope reveals flow-brecciation, broken fragments of the rock lying in 

 a bond of grey translucent chalcedony. 



Sheet No. 2. — This band, about 165 feet thick, has been quarried 

 extensively on the face of the steep crags overlooking Pandy, at Cae 

 Deicws, and in the large quarry opposite Coed-y-Glyn. Indurated 

 slates and grits border the sill on both surfaces, and large masses of 

 slate occur as inclusions. A band of white rock of very varying 

 thickness occupies the middle, which under the microscope shows 

 large idiomorphic quartz and orthoclase felspar crystals in a felsitic 

 ground-mass. The margins are intensely sheared, grey in colour, 

 and include a great number of slate and limestone fragments along 

 with angular pieces of the white uncleaved central portion. 



Sheet No. 3. — This sheet is well seen in Coed Errvvgerrig, and can 

 be traced across the bed of the river to the east side of the valley at 

 Cwra Clwyd. While the main mass resembles Sheet No. 2 in com- 

 position, it includes fragments of quartz felsite, felsite breccias, and 

 nodular rhyolites arranged in parallel bands. 



It is 190 feet thick, and has caused intense metamorphic action on 

 the grits above and slates below. 



Sheet No. 4 is best seen at Hendre Quarry, whei-e it is worked 

 extensively, and locally known as the Glyn ' Granite.' 



It is an analcite-diabase, 96 feet thick, of coarse texture in the 

 middle and finer grained towards the margins. The slates in contact 

 are converted into compact spotted slate. 



Intrusions of similar age and almost identical character have been 

 described from Counties Donegal, Armagh, Wicklow, and other parts 

 of Ireland, and a close parallelism can be drawn between these 

 rocks and those in the Berwyns. The intrusions of Sheets Nos. 1, 2, 

 and 3 probably date from the interval between the deposition of the 

 Bala series and the overlying slates and grits of Wenlock age. No. 4 

 may be of a later date. 



S, S "V IIE "W S. 



I. — The Pal^ontographioal Society. 



THIS Society, founded in 1847 for the publication of monographs 

 on British fossils, has just completed its fifty-seventh volume, 

 for 1903, which is now being issued to subscribers. It is one of 

 the largest and most varied volumes hitherto published by the 

 Society, and is illustrated with no less than 48 plates. It contains 



