Peacock : The Fenland Soils. 



frequent the marsh waters. Over the whole of the ( Black 

 Land ' which fringes the alluvium, and which indicates the spot 

 where the lower peat bed comes to the surface, hundreds of Oak 

 trees lie buried in the peat along- with their ancient flora, or are 

 found rotting into slow decay by the borders of arable fields, or 

 as gate posts, stack props, etc., or are used as fuel where they 

 are dug out. They are exactly the same species as those in the 

 woods and fox covers on the .* topland ' near at hand. 



Along with the peat in some places there is found another 

 deposit in the great Fenland — I mean the Shell Marl. As far as 

 I remember it has not been observed in the portion of the great 

 Fen in this county. It is interesting, however, to us because it 

 is being formed to-day in a little bit of boggy ground at Aylesby, 

 near Grimsby. The Shell Marl is seen best at Whittlesey, 

 Trundle, and Dray Meres, and Walpole Pit, not very far to the 

 south of Spalding, in Huntingdonshire. It is a residual deposit 

 of vegetable decay in pure limewater; I might almost say eumu- 

 lose like the peat by which it is surrounded, only the humus 

 of the plants has been removed. It is a purely sedentary 

 accumulation, and thus widely different from the alluvial silt 

 which has been transported by river and estuarine action from 

 the vast watersheds of the Fen's rivers past and present. The 

 flora of the Shell Marl is simplicity itself — it consists of Characeas 

 and nothing else. I believe that two species only have been 

 detected in it, or as natives of the neighbourhood where it 

 flourished formerly, namely, Chara fcetida and C. hispida. Its 

 Mollusca are the following purely freshwater species : — Bithinia 

 tentaculata, Limncea auricularia, L. peregra, L. stagnalis, Plan- 

 orbis umbilicatus, PL spirorbis, Succinea putris, Sphcerium cor- 

 neum, Pisidiiim amnicum. 



Why it is so restricted in area is rather a difficult matter to 

 settle, or I should say was, before spots where a similar deposit 

 is forming at the present time were discovered. The insuperable 

 difficulty of finding fitting causes and circumstances can be 

 explained by like surroundings in another locality. In Aylesby 

 Bog, which is of most limited extent by the Beck of the same 

 name, south of Great Cotes parish, are a number of ' Blow 

 Wells,' in which marl of the same nature is being formed and 

 deposited annually. The conditions in and around these Blow 

 Wells are as follows : — 



i. — The water is perfectly pure and fully charged with 

 carbonate of lime from having filtered through the chalk, winch 

 lies immediately below the Boulder Clay on which the bog lies. 



1902 June 1. 



