Page:VCH Worcestershire 1.djvu/50

 A HISTORY OF WORCESTERSHIRE The Lower Lias Clay extends over the vale of Evesham, around Pershore and Great Comberton, to the foot of Bredon Hill, and the northern end of the Cotteswolds. Here fertile meadows and pastures characterize the land, but the stiffness of the calcareous clay is much ameliorated by superficial coverings of sand and gravel ; hence the rich fruit grounds and market gardens near Evesham and Pershore. Judging by a deep boring at Mickleton in Gloucestershire the full thickness of the Lower Lias is over 950 feet/ The several beds are distinguished by successive groups of fossils, as noted in 1840 by Strick- land.^ These groups are characterized by species of Ammonites, and although there is nowhere any definite plane of division in the strata, yet it is convenient to subdivide them into zones, because the relative order of succession of the fossils is maintained over wide areas while the lithological characters and the thicknesses of the strata are subject to change. Thus above the limestones before-mentioned, which are character- ized by Ammonites planorbis (or A. johnstoni), we have beds characterized by Ammonites angulatus, A. bucklandi^ and A. semicostatus. These occur further east of the scarp as at Bredon, Defford, and Besford, and again at Evesham and Hampton, at Chadbury, and east of the Littletons. Higher stages yield Ammonites obtusus, A. oxynotus, and A. jameso?ii, as near Pershore, Honeybourne, and Aston Magna ; and again A. capricornus should be found along the northern base of Bredon Hill. A fine series of Lower Lias fossils many of which are now in the British Museum was locally obtained by the late T. J. Slatter, of Evesham.^ Among the more noteworthy of the Worcestershire fossils are Lima gigantea, Gryphcea arcuata, fine examples of Cardinia, and the rugged bivalve Hippopodium ponderosum, also corals of the genus Heter- astrcea. Saline waters have been encountered in shallow wells at Evesham and Hampton Spa. The villages in most cases are supplied from water held in gravel which occurs in patches over the Lias clay, so that the supplies are not always safe from surface pollution. The Middle Lias occupies but small areas in Worcestershire, on the northern and eastern slopes of Bredon Hill, and on the slopes of the Cottes- wolds near Broadway and Blockley. In these situations it is much obscured by debris from the heights above. It is a somewhat variable formation, 250 feet thick, or more, the lower part comprising micaceous loams, clays and sands, while the upper part is a rock bed of ferruginous and sandy limestone, sometimes termed the Marlstone. The clays and loams are characterized by Ammonites margaritatus, and the rock bed by A. spinatus. In this upper bed, which is 8 or ' H. B. Woodward, * Lias of England and Wales,' Mem. Geol. Survey, p. 156. J. Buckman and H. E. Strickland, 1845. 2 See also Wright, ' Lias Ammonites ' {Palaontographical Soc), p. 375; and R. Tate, Quart. Jouin. Geol. Soc., vol. xxvi. p. 396.
 * Proc. Geol. Soc, vol. iii. p. 314 ; see also Murchison, Geo/. Cheltenham, edit. 2, by