472 PROP. T. G. BONNET ON A SECTION 



described, but has less ferrite and a greater proportion of the mica- 

 ceous constituent in rather large folia. The compact purple rock, 

 resembling a flinty argillite, shows a clear matrix, studded with 

 belonitic crystallites of a pale yellowish-green colour and with innu- 

 merable granules of the above-mentioned ferruginous constituent, 

 arranged in wavy parallel bands. The matrix is siliceous, partly 

 chalcedonic quartz and partly, I think, opal. Though the consti- 

 tuents are very minute, the rock appears to be rightly considered a 

 true schist ; and I suspect its abnormal aspect is partly due to a 

 subsequent infiltration of silica. I have compared these slides with 

 specimens from near Menai Bridge, which much resemble the first and 

 third (except that they have a hydrous white mica), and several 

 specimens from the north-west of Anglesey, including those described 

 in my Appendix to Dr. Callaway's paper (Quart. Journ. GeoL Soc. 

 vol. xxxvii. p. 234, Group B). All these have a strong general re- 

 semblance one to another. 



Beyond the last-named schist is an interval of about 60 yards, 

 where every thing is concealed beneath loose soil and vegetation ; 

 and then comes an outcrop of a massive grit, hard, jointed, weather- 

 ing to a brownish colour, and at the first glance rather like one of the 

 intrusive masses of basalt further down the hill. It is at first fine 

 in texture and dark in colour ; then it becomes a little coarser, ancl 

 is full of rolled grains, up to about the size of a small pea, of felspar 

 and felsite, which weather white. More angular fragments of a 

 very compact black rock, up to nearly 2 inches in diameter, now and 

 then occur. These grits are exposed by the roadside for about forty 

 yards ; their dip is not easily ascertained, seemingly it is to the 

 east. There is then an interval of 18 yards covered by vegetation, 

 followed by an exposure of a similar grit for about 16 yards. Another 

 interval of 60 yards succeeds, and we then find a slightly finer grit, 

 which passes into hard blackish and brownish argillite, traversed by 

 small quartz-veins, and looking rather crushed. The dip here ap- 

 pears to be about 25° E. Grits and argillite alternate for about 

 100 yards ; and then, after another interval of about 36 yards, we 

 find a hard argillite, in the middle of which is a greenish grit dip- 

 ping towards the E. and exposed for about 130 yards. 



Rather more than a hundred yards from the last exposure of the 

 above-described rock, the lane already mentioned is crossed by a 

 bridge ; and in the park on the other side we find a considerable area 

 of rounded surfaces of rock, seemingly ice-worn, partly masked by 

 earth. The first reached is a grit (generally similar to the one last 

 seen on the other side of the bridge), banded with greenish and grey- 

 ish argillite ; this soon becomes coarser, and in it may be noted frag- 

 ments of the black rock already described, of a green argillite, and 

 pebbles of the purplish felsite so well known on the other side of the 

 Straits. The dips here appear to be high, and to have changed their 

 direction to the N.W. ; but in deposits of this nature it is not easy to 

 be sure. Then succeeds, sometimes by a very abrupt transition, a 

 coarse purplish grit or conglomerate (the fragments weathering 

 nearly white), full of bits of the felsite. 



In one spot I noted a lenticular patch where the materials sud- 



