A HISTORY OF LEICESTERSHIRE 



The thickness of these shales is about 200 ft., but it varies somewhat in 

 different places. Exposures in them are very rare, and consequently it is 

 only from artificial excavations that the above classification can be made out. 



The Upper Lias usually rises in a steep bank above the terrace formed 

 by the Rock Bed ; and produces an undulating district, much covered by 

 Drift, which extends along the eastern side of the county from Market 

 Harborough to Pickwell. North of Edmondthorpe the outcrop is much 

 narrower, and the ground being covered with a thick deposit of Drift these 

 beds are but obscurely seen. 



The dark shales of the Lias have been mistaken for Coal Measures, 

 which sometimes led in former times to fruitless trials for coal, as was the 

 case at Billesdon Coplow. 1 



That the Lias has been laid down in seas of varying depth is indicated 

 by its fossil contents. The passage from the Rhaetic with fragmentary 

 remains to the lower beds of Lias with Ammonites, Saurians, and Fish shows 

 a gradual change from shallow lagoons to an open sea. The sandy beds of 

 the Middle Lias and the basement portion of the Upper Lias indicate the 

 oncoming of shallower water, which again deepened when the main mass of 

 the Upper Lias clay with its abundant Ammonites was laid down. 



INFERIOR OOLITE 



The Inferior Oolite, which makes such a fine escarpment just beyond 

 the eastern boundary of the county, is but poorly represented in Leicester- 

 shire. Small patches, however, of the rock are found capping hills at 

 Nevill Holt, Loddington, Robin-a-Tiptoes, and Whatborough. North of 

 Melton Mowbray a projecting spur of the main outcrop comes within the 

 district about Waltham-on-the- Wolds and Croxton Kerrial. It comprises 

 two divisions, the Northampton Sand and the Lincolnshire Limestone. 

 The first of these is further sub-divided into the two horizons of the North- 

 amptonshire Ironstone and the Lower Estuarine Series. 



THE NORTHAMPTON SAND 



The Northamptonshire Ironstone is usually a rich ironstone which, when 

 not altered by the percolation of water, is a hard and compact rock of a 

 blue or green colour composed of carbonate and silicate of iron. Under 

 the microscope it is seen to consist of rounded oolitic grains. The rock, 

 when it occurs near the surface and has been exposed to atmospheric 

 influences, exhibits a peculiar cellular structure resembling a collection of 

 oblong boxes. This has been produced by the concentration of hydrated 

 peroxide of iron along the bedding planes and joints, which has split up the 

 rock into roughly rectangular blocks.' 



This ironstone passes up into brown sands, which are succeeded by 

 white sands with occasional layers of clay and lignite. To these upper 

 beds the name Lower Estuarine Series has been given. The total thickness 



1 Life and Letters ofj. B. Jukes, 1871, p. 467. 



' Memoirs of the Geol. Surf. : ' The Geology of Rutland,' 1 1 8, 1 34. 



