THE GEOLOGY OF THE DISTRICT 53 



near Tilton. The Inferior Oolite forms the long, straight Lincoln edge 

 and the scarp near Rockingham, and the thinner limestones overlying 

 that form minor ridges. 



The light soils of the limestone outcrops are much used for agriculture, 

 but the heavy clays of the lower land are now mainly devoted to pasture. 

 The distribution of water-bearing beds has exercised a marked control 

 over the location of villages, particularly in Lincolnshire. 



During the last century, wide use has been made in the Fens of artesian 

 water from the Lincolnshire Limestone, which provides the most im- 

 portant water-bearing beds in this part of the area. 



The ironstones of the Lower Lias are worked at Frodingham, and that 

 of the Middle Lias Marlstone is extensively exploited in Leicestershire. 

 The Inferior Oolite Northampton Ironstone is worked in Northampton- 

 shire, south of Grantham and at Lincoln. 



At the close of the Triassic desert period the greater part of the East 

 Midlands became submerged beneath a sea in which the marine Jurassic 

 deposits were accumulated. 



The first were the Rhaetic beds, which maintain constant characters 

 throughout the area. The lower part consists of 15-20 feet of black 

 shales, which yield Pteria conlorta, Schizodus and Protocardia. Local 

 thin sandy bands occur crowded with fish teeth. The uppen Rhaetic 

 usually consists of 10-20 feet grey-green marls, with scattered limestone 

 nodules, which yield Estheria. Thin ripple-marked sandstones sometimes 

 occur. The White Lias, which forms the highest part of the Rhaetic in 

 the south of England, is unrepresented here. 



The Lower Lias consists mainly of clays, with secondary hmestone 

 bands in the lower part. In Leicestershire the Blue Lias or Hydrauhc 

 Limestones correspond to the Angulatum and Bucklandi zones, as in 

 southern England. The beds below are poorly represented. Further 

 north the Hydraulic Limestone series is of planorbis and preplatwrbis 

 age, and the overlying Angulatum and Bucklandi zones are clayey. The 

 limestones have yielded an interesting fauna, including insects, corals, 

 saurians, fish and Crustacea at Barnstone and Barrow-on-Soar. 



In North Lincolnshire a bed of oolitic iron ore, 30 feet thick, known as 

 the Frodingham ironstone, occurs in the Lower Lias. The base of this 

 bed yields Coroniceras, cf. gmuendense, the middle part contains abundant 

 Cardinia and Gryphea, and during a recent visit to Scunthorpe 

 Aegasteroceras, cf. saggitarium (Blake) and Eparietites colenotii (D'Orb.) 

 (identified by Dr. Spath) were obtained from the upper part. The iron- 

 stone is therefore a greatly condensed deposit, representing 200 feet of 

 beds in the south, for the lower beds belong to the early Bucklandi zone, 

 and the upper part to the Stellare zone. In South Lincolnshire a thin 

 ferruginous limestone is the only lithological representative of this bed, 

 and the presence of Arnioceras belonging to the Bucklandi zone in the 

 overlying clays shows that the greater part of the ironstone has passed 

 laterally into clay. 



The upper beds of the Lower Lias are grey shales and clays, which at 

 Old Dalby have yielded a very rich fauna of ammonites, belemnites, 

 gasteropods and brachiopods. At Bracebridge, near Lincoln, the beds 



