NORTHAMPTON SANDS. 31I 



and ironstone beds is twelve feet ; at Banbury also the beds are 

 twelve feet in thickness. 



The Ironstone-beds yield a number of fossils, many of them, as 

 Mr. Sharp points out, cast, as it were, in iron, so that the introduction 

 of the ore must have taken place subsequently by infiltration and 

 replacement. 



Economic products, etc. 



The iron-ore is worked at Duston, Blisworth, Gay ton, Wellingborough, Cranford, 

 Stamford, etc., and there are blast-furnaces at Neville Holt. The ore yields 40, and 

 sometimes 55 per cent, of pig-iron. The iron-ore has also been worked in several 

 places north and south of Lincoln. According to Prof. Judd, the iron-ore has 

 been formed chiefly by infiltration of waters containing carbonate of iron in 

 solution.'- Allophane has been met with near Northampton. 



In places the Northampton Sand contains hard calcareous sandstone which has 

 been used for building-purposes ; while some beds are sufficiently calcareous for 

 lime-burning. The White Sands are dug for making mortar. Clay-beds in this 

 series have been worked for brick-making, and for Terra-cotta in the neighbour- 

 hood of Stamford-Baron. Concretionary masses of sandstone called ' Pot-lids ' are 

 met with in the sands. At Duston, near Northampton, beds of fissile sandy 

 limestone were formerly dug for roofing-purposes under the name of the " Duston 

 Slate." 



Capt. Macdakin mentions that immediately over the Upper Lias Clay south of 

 Lincoln there is a curious bed (three inches in thickness) of phosphatic nodules, 

 with masses of pyrites, which the country people carry off as decorations for their 

 chimney pieces.^ The Northampton Sand forms a rich soil. 



CoUyweston Slate. 



At CoUyweston, south-west of Stamford, certain fissile calcareous 

 sandstones, or sandy limestones, which, after exposure, split up 

 horizontally and form flagstones or tilestones, have been quarried 

 for roofing-purposes, and are termed the CoUyweston Slates. 

 Where thickest the beds are a little over eighteen feet. Prof. Judd 

 observes that sometimes the sands which alternate with these 

 lower beds of sandy limestone at the base of the Lincolnshire 

 Oolite are full of calcareous concretions, the associated limestones 

 exhibiting broad mammillated surfaces, which give rise to the 

 masses known to quarrymen as " pot-lids." ^ 



The CoUyweston Slates overlie the Northampton Sands, and are 

 overlaid by the Lincolnshire Limestone ; and as there is a general 

 resemblance between these CoUyweston tilestones and the Stones- 

 field Slate, they were at one time confounded. The CoUyweston 

 Slates may partly represent the Lower Estuarine beds which overlie 

 the Dogger in Yorkshire.* 



^OC)^ 



Geol. Rutland, etc. (Geol. Survey), p. 11; 



G. Mag. 1877, p. 406. 



Geol. Rutland, etc., p. 140. 



J. Morris, G. Mag. 1869, p. 104. 



