Geological Society of London. 45 



4. "On the Stratigraplucal Position of the Lower and Middle 

 Jurassic Trigomce of North Oxfordshire and adjacent districts." By 

 Edwin A. Walford, Esq., F.G.S. 



The author spoke of the value of the Trigonim as stratigraphical 

 guides and of the wealth of the Oolitic deposits of North Oxfordshire 

 in number of species as well as of individual forms. He alluded to 

 the recent discovery by Northampton geologists of Trigonia literata 

 and T. pulchella in the centre of their county. By the jDresence of 

 certain Trigonice as well as of corals and bored stones he endeavoured 

 to prove the extension of a stratum at the base of the Clypeus -gv'it 

 at Fawler, as far as Hook Norton, also in North Oxfordshire, where 

 the bulk of the Inferior Oolite was of an altogether different type. 

 In Mr. Walford's list were nearly thirty species and varieties from 

 the Bajocian beds. To the lower horizons there belonged but one 

 local form and no species of special stratigraphical value. The 

 presence of a few other fossils supposed to be characteristic was the 

 only evidence of beds below the zone of Ammonites MiircMsomce. 

 Series C, which appeared to be of the age of the lower Trigonia- 

 grit, had yielded the greater part of the TrigonicB mentioned, several 

 of them being peculiar to the horizon, whilst others were local 

 species. The higher beds had yielded some apparently undesci-ibed 

 forms, whilst hitherto unrecorded species were quoted from the 

 Great Oolite and Forest Marble. One species (T. Lycettii) was 

 described as new. 



IL— December 3, 1884.— Prof. T. G. Bonney, D.Sc, LL.D., F.E.S., 

 President, in the Chair. The following communications were read : 



1. " Note on a Section near Llanberis." By Prof. A. H. Green. 



In this paper the author described a section showing actual un- 

 conformity at the base of the Cambrian. In one of the cuttings on 

 the railway that runs from the Dinorwig quarries along the north- 

 western slaore of Llyn Padarn, the basement conglomerate of the 

 Harlech and Llanberis group, dipping N.W. at a moderate angle, 

 rests upon vertical slaty beds, one of which is a breccia. The author 

 believes that the section described is one of which a different readiuc'- 

 was given by Sir A. Eamsay in the Geological Survey Memoir on 

 North Wales. In that work the conglomerate was regarded as a con- 

 tinuation of the breccia of the underlying beds sharply turned over. 



The microscopic characters of the lower series show that these beds 

 are probably coarse volcanic tuffs, and that they resemble the rocks 

 at St. David's, called Pebidian by Dr. Hicks. The unconformity 

 observed does not necessarily indicate great difference of age between 

 the conglomerate and the underlying beds. In volcanic rocks such 

 breaks may be merely local. 



Further north-west, in the same railway section, a junction is seen 

 between the Cambrian conglomerate and quartz-felsite. It is uncer- 

 tain whether the junction is a fault or not. The matrix of the con- 

 glomerate is chiefly composed of felsite fragments so perfectly 

 cemented together as to bear a close superficial resemblance to the 

 original rock even under the microscope, unless a high power be used. 



2. "The Tertiary Basaltic Formation in Iceland." By J. Starkie 

 Gardner, Esq., F.L.S., F.G.S. 



