HARD WICKE' S S CIE NCR ■ G O SSIP. 



265 



THE GEOLOGY OF THE LINCOLNSHIRE MARSHLAND. 



By A. J. JUKES-BROWNE, B.A., F.G.S., etc. 

 [Continued from p. 245.] 



ET my readers ima- 

 gine all I men- 

 tioned in my last 

 article as taking 

 place on the Lin- 

 colnshire coast 

 before the marsh- 

 land was formed, 

 and when the edge 

 of the chalk wolds 

 was presented to 

 the sea as a bold 

 line of cliffs, from 

 which quantities 

 of chalk rubbish 

 fell on the ice-foot 

 below : outside 

 they must imagine 

 a sea full of ice- 

 bergs and ice-floes 

 borne southwards 

 from more northerly shores, and when driven by 

 storms upon the coast adding their foreign freights 

 of mud and stones to the local material out of which 

 the gravels and boulder clays were being made. By 

 picturing this state of things, they will understand 

 how these peculiar deposits came into existence, why 

 they are laid down so unevenly and irregularly, why 

 their surface presents so many mounds and hummocks, 

 why they are so full of pieces of chalk, and how the 

 large blocks and boulders of other rocks came to be 

 mixed up together in the same formation. 



These glacial conditions lasted for a long time, 

 but gradually the winters became less severe and the 

 summers longer, if not warmer, the ice melted away 

 and left its last burden of mud and stones to form 

 the surface of the rolling hummocky ground which 

 now rose gradually from the waves and stretched far 

 eastward beyond its present limits over the ground 

 now occupied by the marshes and far out into the 

 German Ocean. But change, ceaseless change and 

 movement, is ever Nature's order of the day, and 

 No. 180. 



before long a reverse movement of depression set in 

 which enabled the sea-waves to attack this rolling 

 plain of boulder clay, and eventually to destroy the 

 greater part of it, gradually eating back its edge, till 

 only a narrow strip remained which now separates 

 the wold from the marshes. 



Without stopping to inquire what prevented its 

 entire destruction, we content ourselves with observing 

 that some change occurred, possibly in the set of the 

 currents along the shore, which checked the process 

 of erosion and prevented the rapid removal of the 

 material gained from the land. The result of this 

 change would be to cause the formation of sandbanks, 

 and the silting up of the bays and inlets along the 

 coast line, and thus were formed the silts and 

 clays, which lie at the bottom of the marsh deposits 

 (or Post-glacial beds) shown in the section of the well 

 at Mablethorpe. 



The reason of the greater thickness of the glacial 

 clays at Anderby can now be understood ; this place 

 is in close proximity to a promontory of boulder clay, 

 which for some reason did not suffer so much erosion 

 as other portions of the formation to the northward. 

 This district must therefore have continued to remain 

 above water, while the lower beds of the post-glacial 

 series were deposited at Mablethorpe ; and some parts 

 of it were never altogether submerged, but even now 

 form low mounds rising above the level of the 

 surrounding marsh. 



The submergence above spoken of did not continue 

 without cessation, but there were probably pauses 

 during which the land was stationary for some time, 

 and when the silted up shore gradually passed into 

 the condition of a salt marsh just as such marshes are 

 being formed at the present time along the shores of 

 the Wash. The vegetation which would flourish and 

 decay in such places, furnished the black peaty matter 

 occurring in the upper part of these marsh clays ; 

 while the beds of turf or peat, with trunks of trees 

 which are found in many places, prove that large 

 forests grew and decayed on the higher parts of this 

 marshy land ; but the overlying beds of clay and silt 



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