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 Ilarpoceras Murchisona), 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-bed {Zone of Lytoceras Jtirense), 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 



T)'. A thin seam of yellowish sand IJ 



E. 



V. 



Upper Lias Sand and Clay. 



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

 Carboniferous Limestone ; it is bored in difi"erent 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 ? 



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



Fossils of the Pea-c/rit and Freestones. 



Cephalopoda. 



Harpoceras Murchisonse, Sow. 

 Nautilus truncatus, Sow. 



Belemnites spinatus, Quenst. 

 — abbreviatus. Mill. 



Gasteropoda. 



Patella rugosa, Sow. 



— inornata, Lijc. 



Pileolus Isevis, Sow. 



Nerita costata, Sow. 



— minuta. Sow. 



Monodonta Lyelli, it Arch, 



— sulcosa, d'Arch. 



Natica adducta, Phil. 



Cirrus nodosus, Sow. 

 Trochotoma carinata, Lye. 

 Turbo elaboratus. Lye. 

 Trochus monilitectus, Phil. 

 Solarium Cotswoldise, Lye. 

 Nerinsea cingenda, Bronn. 

 Actseonina Sedgvici, Phil. 

 Alaria spinifera, Lye. 



