54 SCIENTIFIC SURVEY OF NOTTINGHAM AND DISTRICT 



of the Davoei zone contain abundant well preserved capricorns, and 

 inflated ammonites of the Liparoceras type. A thin ironstone band 

 occurs at this level in North Lincolnshire. 



The lower part of the Middle Lias (Margaritatus zone) consists of grey 

 clays, occasionally sandy, with ironstone nodules. The beds measure 

 nearly 100 feet in Leicestershire, 56 feet at Grantham, 30 feet at Lincoln, 

 and probably thin out a little more farther north. The Spinatum zone is 

 represented by the marlstone ironstone, which may be as much as 40 feet 

 thick. The ironstone is well developed north and south of Melton Mow- 

 bray, but it is very thin north of Market Harborough and is absent for 

 15 miles north and south of Lincoln. It is noticeable that where the 

 marlstone is attenuated Dactylioceras has been recorded (Ingham, Leaden- 

 ham, and north of Market Harborough), showing that the attenuation is 

 due to the failure of the lower part of the bed. The fauna of the iron- 

 stone includes Lobothyris punctata, Tetrarhynchia tetrahedra, Pteria 

 inaequivalvis and Belemnites elongatus. The zonal ammonite is very 

 rare. Locally a thin bed with Tiltoniceras and dactyliocerates occurs at 

 the top of the ironstone. 



The upper Lias consists of 100-200 feet of dark shales and clays with 

 scattered nodules. Study of the fauna shows that the lower beds are 

 thickest at Lincoln, the middle beds reach a maximum at Grantham and 

 the upper beds are best developed in Northamptonshire. The fauna 

 shows a mixture of Yorkshire and southern forms. Various species of 

 Harpoceras and Dactylioceras are common. 



Resting nonsequentially on the Upper Lias is the Northampton iron- 

 stone, 10-20 feet thick, a green oolite ore which weathers to a brown 

 ferruginous sand. It has been shown that the material forming this bed 

 came from a land mass southeast of Kettering. Unhke the Lias iron- 

 stone, this bed is usually unfossiliferous, but Lioceras spp, Hinnites 

 velatus, Trigonia spp. and various brachiopods occur at certain places. 

 In North Lincolnshire this ironstone is represented by 2 feet of ferruginous 

 sandstone, which has recently yielded brachiopods of scissum age. The 

 Northampton Ironstone is succeeded nonsequentially by the Lower 

 Estuarine Series, a variable thickness of pale sands and clays with vertical 

 plant remains. Determinable fossils are almost entirely absent from 

 these beds. 



The most important member of the Inferior Oolite Series is the Lincoln- 

 shire Limestone, which first appears at Kettering and thickens to a 

 maximum of 140 feet south of Grantham. The greater part of the lime- 

 stone is ooUtic, but raggy beds occur locally in the upper part, and in 

 North Lincolnshire the lower part of the formation passes into a cement- 

 stone series (the Kirton Beds). At the base of the limestone, near Stam- 

 ford, are thin sandy beds, which yield siliceous flags known as Collyweston 

 Slates. These beds are overlapped towards the south. Ammonites have 

 shown that the base of the limestone is of discites age, and brachiopods 

 indicate that the whole of the Bajocian and part of the Vesulian are 

 represented by the Umestone. The various epiboles maintain a constant 

 thickness as traced along the outcrop, and the variation in thickness of 

 the limestone depends almost entirely on the amount of pre-Bajocian 

 denudation. P.E.K. 



