Jurassic Strata beticeen Filton and Wootton Bassett. 175 



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

 must be classed as ort ho gneisses, 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 endoinorphic 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 Prof. Sidney 

 Hugh Reynolds, M.A., F.G.S., and Arthur Yaughan, Esq., B.A., 

 B.Sc, F.G.S. 



In this section a thin bed of typical Cotham 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 Planorb is-beds, containing the 

 Ostrea-be&s and the Oidaris-shales ; (2) the Angulatus-be&s, in- 

 cluding the Conybeari sub-zone ; (3) probably the Bucklandi-hed ; 

 (4) the Tumeri-sholes ; (5) the Oxynotus-beds ; (6) the Armatus 

 and Jamesoni-be&s ; and (7) the Oapricornus-zone. 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. 

 striatidus. 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 

 4 Pea-Grit ' followed by oolitic limestones and ' Trigonia-Grit.' It 

 is succeeded by an oolitic limestone of considerable thickness 

 containing fossils of the Pullers' Earth type, and forming a passage 

 between the Inferior Oolite and the Fullers' Earth, which comes 

 next in succession. Above this are sandy limestones, passage-beds, 

 with Amm. gracilis, a form found in the Stonesfield ' Slate." The 

 Great Oolite consists of white oolitic limestones with a Pholadomya- 

 bed below, and an upper series of wedge-bedded oolitic limestone- 

 containing lenticular patches of clay and sand with a Bradford- 

 Clay fauna. The Forest Marble, which is of great thickness and 

 ^monotonous character, consists chiefly of shales, with bands o( 

 sandy, shelly, and oolitic limestones. It is followed by the Corn- 

 brash. The Oxford Clay with the usual zones, and the Corallian 

 clays and pisolite close the sections. Fossil lists and palseontological 

 notes on each subdivision are given. 



