426 Reports and Proceedings — Geological Society of London. 



The chief rock-types vary from basic pyroxene-sphene-scapolite- 

 rock, through intermediate rocks composed of pyroxene, scapolite, 

 and wollastonite, with felspar and quartz subordinate or abundant, 

 to acid types made up of orthoclase-microperthite or coarse-grained 

 quartzo-felspathic rocks. They differ from the normal types be- 

 longing to the CharnocUite Series in their somewhat coarser grain, 

 in the presence of wollastonite, scapolite, and sphene, the existence 

 of definite dykes and segregation-veins crossing the foliation, and in 

 the absence of garnet, hypersthene, original mica, and hornblende ; 

 but they resemble the series in the variability of chemical and 

 mineralogical composition, in the conspicuous foliation, the common 

 strike, the petrological character of the acid types, and in the local 

 tendency to graphic structures. The foliation, dykes, weathering, 

 and relationship to the Charnockite Series are described : and an 

 account is given of the more important of the minerals. The rocks 

 must be classed as orthogneisses, and the wollastonite and scapolite 

 are original minerals. Possibly the richness in lime is due to the 

 absorption of a mass of limestone by a portion of the Charnockite 

 Series. If this be the case, the lime-silicates must be regarded as 

 endomorphic contact-minerals. On the other hand, the local richness 

 in lime might be due to an original variation in the constitution of 

 the magma. The rocks show a progressive differentiation from basic 

 to acid types, the coarse segregation-veins being the last product of 

 the process. That the rocks have not suffered from earth-movement 

 since their complete consolidation is evidenced by their microscopic 

 characters, while the interlocking of the minerals at the junction of 

 the segregation-veins with the matrix shows that the veins are 

 of contemporaneous character. 



3. " On the Jurassic Strata cut through by the South Wales Direct 

 Line between Filton and Wootton Bassett." By Professor Sidney 

 Hugh Eeynolds, M.A., F.G.S., and Arthur Vaughan, Esq., B.A., 

 B.Sc, F.G.S. 



In this section a thin bed of typical Gotham Marble is followed by 

 the ' White Lias,' and that by the Lower Lias, which in this district 

 attains a thickness of about 200 feet. The following zones are 

 represented : (1) the PZanor6zs-beds, containing the Osirea-beds and 

 the Cidan's-shales ; (2) ihQ Angulatus-hQA^, including the Conybeari 

 sub-zone ; (3) probably the Buchlandi-hed ; (4) the Turneri-shsile& ; 

 (5) the Oxynotiis-heds ; (6) the Armatus and Jamesoni-hed?, ; and 

 (7) the Capricorniis-zoxie. The strata are remarkably shaly, limestone 

 being predominant only at the base. The typical ironshot Marlstone 

 is only a few feet thick, and the Upper Lias is reduced to a thickness 

 of about 10 feet. The latter consists of a compact, cream-coloured 

 marl with Ammonites falcifer, a compact marly limestone with Amm. 

 communis, and a pyritic bed containing Amm. bifrons. The Cotteswold. 

 Sands are 185 feet thick, and contain, at several horizons, hard marly 

 beds with Amm. striatulus. They are capped by the Cephalopod Bed, 

 in which Mr. S. S. Buckman has recognized four Ammonite-zones. 



The Inferior Oolite has at its base a rock on the horizon of the 

 ' Pea-Grit ' followed by Oolitic limestones and ' Trigonia-Gvit' It is 



