GEOLOGY 



of the group is variable, but Mr. A. J. Jukes Browne states that it does 

 not exceed 40 ft. in this district. 1 



THE LINCOLNSHIRE LIMESTONE 



The Lincolnshire Limestone is rather variable in character ; in some 

 places it forms beds of valuable freestone, but in others it is a coarse shelly 

 ragstone interstratified with soft marly or oolitic limestone. Professor Judd 

 has pointed out that the Lincolnshire Oolite presents two aspects which 

 may be specially characterized." A ' coralline facies ' which is characterized 

 by beds of slightly argillaceous limestone, of compact, subcrystalline, or but 

 slightly oolitic texture, abounding with corals, which are usually converted 

 into masses of finely crystalline carbonate of lime. These limestones afford 

 evidence of having been true coral reefs ; they contain shells which 

 are particularly characteristic of this facies. The other variety has 

 been termed the ' shelly facies.' It consists almost wholly of small 

 shells or fragments of shells, sometimes waterworn and sometimes encrusted 

 with carbonate of lime. Small gasteropods are abundant, but are usually 

 waterworn ; the bivalves occur usually as single valves, and are frequently 

 eroded and broken. These beds were evidently banks of dead shells accumu- 

 lated near the coral bed, under the influence of varying currents. 



The ferruginous beds of the Northampton Sand form a rich red soil, 

 which is specially adapted for the growth of crops, while the soil over 

 the Lincolnshire Limestone is also mostly in arable land ; but the outcrop in 

 this district is so limited and so frequently covered by Boulder-clay that 

 the underlying rock has not much effect on the character of the soil. 



GLACIAL DRIFT, VALLEY DEPOSITS, AND ALLUVIUM 



After the deposition of the Oolites an immense break takes place in the 

 series of beds that are found in this part of the Midlands. Although 

 higher beds of Oolite and the Cretaceous Rocks come on in regular succes- 

 sion further to the east and probably at one time covered most of this 

 district, they have now been completely removed by denudation, and there 

 is no trace left of any of these rocks or of the Tertiary strata which play 

 so important a part in the eastern counties and around London. Great 

 changes took place during this period in which the present surface was first 

 mapped out, although it has been subsequently much modified by the action 

 of moving masses of ice, rain, and rivers. After this long period the first 

 evidence of fresh deposition in this district is that afforded by the boulder- 

 clays and gravels, which irregularly overlie the older beds, and are found over 

 the greater part of the area. These beds may be conveniently divided under 

 the separate heads of Glacial Drift, Valley Drift, and Alluvium. 



GLACIAL DRIFT 



The glacial beds which occur in this district are of considerable interest 

 from the fact that they illustrate the character of these beds over a large 



1 Memoirs of the Geol. Surv. : ' The Geology of the South-west part of Lincolnshire,' 45. 

 ' Ibid. 'The Geology of Rutland,' 139. 



