Farming of Lincolnshire. 



279 



been made known respecting the soils of this district, and a great 

 variety of facts have therefore been collected for the purpose of 

 attemptins: here to elucidate the structure and origin of the fens, 

 of which details only the general results can be brought forward 

 at the present time. 



The Oxford and Kimmeridge clays form the great pan 

 on which the alluvial accumulations principally rest, — not 

 only dipping under the fen lands from the north and west, 

 but in many places (as March, Whittlesey, Thorney in Cam- 

 bridgeshire, and Kyme in this county) swelling up through 

 them in the shape of low hills, generally covered by thick de- 

 posits of gravel or brown drift clay. This great bed of clay, with 

 the incumbent sand and gravel, rarely forms the surface or imme- 

 diate subsoil of the flat land, except near the high lands, but 

 undulates beneath the fens, being much further from the surface 

 in some localities than in others. At Boston, 11 miles from the 

 western hills, where the Oxford clay descends, it is found at the 

 depth of about 38 feet from the surface. The unevenness of its 

 surface is undoubtedly the effect of denudation by water ; and it 

 appears to have formed the bed of a spacious bay, on w^hich have 

 accumulated the alluvial beds, — raising the surface up to one 

 uniform level. The subterranean gravel might be supposed to 

 have been washed into this bay by the ordinary action of the 

 tides, were it not connected with similar beds upon the neigh- 

 bouring uplands and the islands " in the fens, at an elevation 

 far above the reach of the present oceanic waters. The first or 

 lowest of the alluvial deposits appears to be silt, — a wet muddy 

 sand, hard and blue at its greater depths, softer and w^hiter in its 

 upper portions. This does not extend under the whole of the 

 fens, but it has been found below all the other alluvial beds. It 

 is evidently the ancient bottom of the great bay, having been a 

 wide expanse of irregular sand-banks like those which are now 

 choking the existing estuary. It is laminated in its upper parts, 

 thus exhibiting a tidal structure, and abounds with cockles and 

 other marine shells. The silt seems in some places to have 

 been accumulated on a shore, and elevated into mounds or ridges 

 like those upon the coast at Skegness and other places, where 

 the sand is drifted by the winds into hillocks above the flow of 

 the tides, and bound into a compact mass by the creeping roots 

 of the arundo arenaria. It is thus found piercing the super- 

 age of the various deposits above the drift beds may be computed. Between the allu- 

 vium and the older strata occurs an immense subterranean forest, with trees standing 

 as they grew upon ground many feet lower than the sea at high tide ; a circumstance 

 apparently indicating a comparatively recent alteration in the relative levels of land 

 and water, which will explain the phenomena of similar submarine, &c. forests (more 

 modem than the drift) on many parts of the coast of Lincoln, York, Norfolk, Kent, 

 Dorset, Somerset, &c., &c. 



