152 



THE LIAS AMMONITES. 



beds are the best for building-purposes ; the middle beds are of an inferior quality, and 

 are stained in part with ferric oxide ; the lower beds, called " Roestone," contain large 

 oolitic grains ; the freestone in all is about 110 feet in thickness. 



The Pea-grit {Zone of Harpoceras Murcliisonce), Inferior Oolite. 



Ft. in. 



A. A brown, coarse, rubbly oolite, full of flattened concretions cemented together by a cal- 



careous matrix. When the blocks weather, the concretions, which resemble flattened 



peas, form a very uneven surface. It contains many fossils in good preservation 12 



B. A hard, cream-coloured, pisolitic rock, made up of flattened concretions, with a thickness 



about similar to those in a 10 



c. A coarse, brown, ferruginous rock, composed of large oolitic grains ; it is readily disin- 

 tegrated by the frost, and is of little economical value. About 20 



The Cephalopoda-led {Zone of Lytocerass Jurense), Upper Lias. 



D. A brown marly rock, full of small dark oolitic grains of the hydrate of iron, which are 



strewed in profusion in a calcareous paste. About 2 



d'. a thin seam of yellowish sand l-f 



Upper Lias Sand and Clay. 



E.. A dark-grey crystalline- limestone, extremely hard, and resembling some beds of the 

 Carboniferous Limestone ; it is bored in different places by Fistulana ? the shells 

 of which remain in the excavations. Thickness not exposed ? 



1'. A brown, argillaceous, sandy bed, full of micaceous particles ; passing downwards into fine 



brown and yellow sands. Thickness unknown 1 



G. Upper Lias clay, of a dark blue colour. Thickness probably , ICO 



Fossils of the Pea-grit and Freestones. 

 Cephalopoda. 



Harpoceras Murchisonse, Bow. 

 Nautilus truncatus. Bow. 



Patella rugosa. Sow. 

 — inornata. Lye. 

 Pileolus Isevis, Sow. 

 Nerita costata. Bow. 

 — minuta. Bow. 

 Monodonta Lyelli, d' Arch, 



— sulcosa, cfArch. 



Natica adducta, Phil. 



I Belemnites spinatus, Quenst. 



I — abbreviatus. Mill. 



Gasteropoua, 



I Cirrus nodosus. Bow. 



Trochotoma carinata, Lye. 

 Turbo elaboratus, Lye. 

 Trochus monilitectus, Phil. 

 Solarium Cotswoldise, Lye. 

 Nerinsea cingenda, Bronn. 

 Actseonina Sedgvici, Phil. 

 Alaria spinifera. Lye. 



