ZONE OF HARPOCERAS SERPENTINUM. 117 



of Rutland,' p. 79, 1875. "Jet Rock series^ Zone of Ammonites serpentinus," Tate 

 and Blake, 'Yorkshire Lias,' p. 73, 1876. 



The argillaceous beds of this zone in Gloucestershire consist of bluish clay, containing 

 occasional and irregular bands of nodular argillaceous limestone resembling " cement- 

 stones." In the escarpments of the Cotteswold Hills the Serpenfinuin-zowe of the Upper 

 Lias attains in some places a thickness of 80 feet, interposed between the Marlstone or 

 rock-bed of the Margantatus-TiOW& and the beds with Harpoceras lifrons. The Upper 

 Lias clay is generally concealed by debris derived from the Oolitic strata, and its position 

 is therefore most readily ascertained by surface indications, such as springs and marshes. 

 This clay-bed forms the retentive water-bearing stratum at the base of the superincumbent 

 porous strata, so that the rain, which falls upon the table-land of the Cotteswold Hills, 

 after saturating the Oolitic rocks and subjacent sands, bursts forth as springs along their 

 slopes and escarpments, at the junction of these beds with the impervious clay. All the 

 springs in this district arising from the drainage of the Inferior Oolite have their origin 

 in this arrangement of the strata, and break out as sources at an elevation of about 

 700 feet above the level of the sea. 



On the summits of Bredon, Alderton, Gretton, and Churchdown Hills, all outliers of 

 the Cotteswolds, we find sections of the Serpentinum beds, wliich consist in general of the 

 following subdivisions : 



1st. Brown marly clays of variable thickness, according to the extent of denudation 

 of the upper beds ; they contain many of the fossils of our list. 



2nd. A band of nodular argillaceous limestone, from six to eight inches in thickness, 

 called the " Fish-bed ;" this stratum has yielded many interesting remains. I obtained 

 from a nodule at Gretton a large and nearly perfect specimen of P achy cor m us latirosfris, 

 Ag., and from nodules at Alderton, Dumbleton, and Gretton have been extracted 

 Leptolepis concentricus, Egert., Tetrat/onolepis discus, Egert. Wings and elytra of Insects 

 have been found in nodules at Dumbleton and Gretton, of which the most remarkable is 

 a fine Neuropterous wing belonging to Lihellula Brodiei, Buck. 



3rd. Is a thick bed of bluish mottled clay, several feet in thickness, and more or less 

 laminated, at Alderton, where I saw it many years ago well exposed; it contained a great 

 many small Gastropods, among them were CeritJmim, Bostellaria, Trochus, and Nalica ; 

 of Lamellibranchs, I found Area, Leda, and Posidonomi/a ; of Echinoderms I observed 

 Acrosalenia crinifera, Quenst., Pseudodiadema Moorei, Wrt., Opinoderma, n. sp., and 

 fragments of Pentacrinus. The shells were compressed moulds, which looked beautiful 

 when the clay was first split open, but as it dried, the fossils unfortunately broke into 

 fragments and could not be preserved for specific determination. 



4th. The Leptsena-bed, composed of a brown friable marl, one to two inches thick, 

 contains many species of small Brachiopods, belonging to the genera Lepttsna, Spiriferina, 

 Terehratula, Uhynchonella, and is separated from the upper beds of the Marlstone by — 



