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.
