234 Morris — Geological Excursion to Bath, j-c. 



afforded the party some new and highly interesting sections; one 

 about two miles out, exposed the Ehsetic strata, with so-called Gotham 

 Marble, White Lias, and " Sun-bed," with few fossils, overlain by the 

 Ammonites angidaius, and Bucldandi beds, containing many fossils, 

 noticed by Mr. Moore,^ the section presenting two faults or displace- 

 ment of the rocks. Not far distant is the Twerton Coal-pits sunk 

 through the overlying but unconformable lower Secondary strata of 

 no great thickness ; and it was interesting to observe close to the 

 pit's mouth another fine stone quarry in the Am. Bucldandi beds 

 overlying the probable equivalents of the Am. planorlis zone,^ the 

 former containing the characteristic Lima gigantea, GryphcBa incurva, 

 Nautilus lineatus, Fleurotomaria Angh'ca, etc., and consisting of thick- 

 bedded limestones, with intercalated shaly bands, some containing 

 Foraminifera. In the uppermost portion of the Am. Bucklandi beds 

 of this pit is a thin band of brown indurated marl, indicating a 

 persistent horizon at the top of the series throughout the district. It 

 contains many plants and remains of fishes {Hyhodus, Acrodus, Lepi- 

 dotus, etc.,) as well as Avicida ineqmvalvis and other shells. 



A section on the same railway near Saltford afforded a fine expo- 

 sure of the Am. Bucklandi bed with the associated fossils, showing 

 bands of tabular and septaroid limestone, the latter frequently 

 containing large Ammonites, while fissures were lined with beau- 

 tiful crystals of brown calcite, presenting both the dog-tooth and 

 rhombohedral forms, as well as modified octohedrons of pyrites. 

 The Ammonite is found here in the same condition as the large one 

 originally obtained by Dr. Buckland from the neighbourhood, having 

 lost the inner whorls, which enabled the Doctor to thrust his head 

 and shoulders through, and thus he rode home, dubbed by his friends 

 the Ammon Knight, encircled with the species which now bears his 

 name (Sow. Min. Con. 2, p. 69). 



The party visited, on the railway above-mentioned, at Willsbridge, 

 another fine section, showing the curved strata of the Eed Marl, 

 Eha3tic beds, and Lower Lias faulted against a mass of Pennant rock, 

 or sandstone, deeply ferruginous at the junction, but further on 

 intercalated with carbonaceous layers and bands of red Hematite. 

 The conditions of this section are very instructive, as at the south 

 end is seen the Eed marl with greenish bands, and nodules of 

 celestine (sulphate of strontian) superposed by a fair development 

 of the Eh^tic series with the Avicula contorta zone, Estheria and 

 Oythere shales and White Lias, with Modiola, overlain by the Am. 



1 Geol. Journal^ vol. xxiii. p. 497. 



2 The term zone is applied to a subdivision of Lias strata characterized by the 

 abundance of a peculiar Ammonite and associated fauna, but which are not entirely 

 restricted to that zone. The following are the subdivisions of the Lias, shewing the 

 Ammonite zones : — 



Upper ( Am. Juremis 

 Lias \ A. communis 

 {A. spinatus 



Middle J ^- ^''^^^.^'•^■^^^"* 

 T s -^' caprtcornus 



A. ibex 

 [a. Jamesoni 



Lower 

 Lias 



A. raricostatus 

 A. oxynotus 

 A. obticsus 



•^ A.. Turneri 

 A. Bucldandi 

 A. angulatus 



(^ A. planorbis 



