: Notes on the Fenland; with A Description of the Shippea Man by Hughes Thomas McKenny Macalister Alex Alexander Contributor - Geology England Bedford Level

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e circumstances which are of importance to note with a view to the interpretation of the results observed in the Fens.

For instance in fine weather there is a constant lifting and floating of the confervoid algae which grow on the muddy bed of the stream. This is brought about by the development of gas under the sun's influence in the thick fibrous growth of the alga. The little bubbles give it a silvery gleam and by and by produce sufficient buoyancy in the mass to tear it out and make it rise to the surface dropping fine mud as it goes and thus making the water turbid. Other plants, such as Utricularia, Duckweed, etc., have their period of flotation, and in the "Breaking of the Mere" in Shropshire we have a similar phenomenon. In the "Floating Island" on Derwentwater the same sort of thing is seen with coarser plants. All these processes are going on in the meres and in the streams which meander through the Fens and did so more freely before their reclamation. But besides this, when the top of the spongy peat is raised above the water level and dries by evaporation, then heath, ferns and other plants and at last trees grow on it, until accident submerges it all again.

This at once shows why we often find an upper peat with a different group of plant remains resting upon a lower peat with plants that grow under water.

The most conspicuous examples of these various kinds of peat we see in the mountainous regions of the North and West, where the highest hills are often capped with peat from eight to ten feet in thickness, creeping over the brow and hanging on the steep mountain sides. Sometimes, close by, we see the gradual growth of peat from the margin of a tarn where only water-weeds can flourish.

The "Hill Peat" is made up of Sphagnum and other mosses and of ferns and heather.

The "Tarn Peat" of conferva, potamogeton, reeds, etc.

As Hill Peat now grows on the heights and steeps where no water can stand and Tarn Peat in lakes and ponds lying in the hollows of the mountains and moors, so the changes in the outfalls and the swelling and sinking of the peat have given us in the Fens, here the results of a dry surface with its heather and ferns and trees, and there products of water-weeds only, and, from the nature of the case, the subaerial growth is apt to be above the subaqueous.

One explanation of the growth of peat under both of these two very different geographical conditions is probably the absence of earthworms. The work of the earthworm is to drag down and destroy decaying vegetable matter and to cast the mineral soil on to the surface, but earthworms cannot live in water or in waterlogged land, and where there are no earthworms the decaying vegetation accumulates in layer after layer upon the surface, modified only by newer growths. Some years ago a great flood kept the land along the Bin Brook under water for several days and the earthworms were all killed, covering the paddock in front of St John's New Buildings in such numbers that when they began to decompose it was quite disagreeable to walk that way. It reminded me of the effects of storm on the cocklebeds at the mouth of the Medway, where the shells were washed out of the mud, the animals died on the shore and the empty shells were in time washed round the coast of Sheppey to the sheltered corner at Shellness. Here they lie some ten feet deep and are dug to furnish the material for London pathways.

In those cases when the storm had passed the earthworms and the cockles came again, but the Hill Peat is always full of water retained by the spongy Sphagnum and similar plants, and the Fens are or were continually, and in some places continuously, submerged and no earthworms could live under such conditions.

The blackness of peat and of bog-oak may be largely but certainly not wholly due to carbonaceous matter. Iron must play an important part. There is in the Sedgwick Museum part of the trunk of a Sussex oak which had grown over some iron railings and extended some eight inches or more beyond the outside of the part which was originally driven in to hold the rails. Mr Kett came upon the buried iron when sawing up the tree in his works and kindly gave it to me. From the iron a deep black stain has travelled with the sap along the grain, as if the iron of the rail and the tannin of the oak had combined to produce an ink. The well-known occurrence of bog-iron in peat strengthens this suggestion. An opportunity of observing this enveloping growth of wood round iron railings is offered in front of No. 1, Benet Place, Lensfield Road.

The trees in the Fens often lie at a small depth and when exposed to surface changes perish by splitting along the medullary rays.

It is not clear how long it takes to impart a peaty stain to bone, but we do find a difference between those which are undoubtedly very old and others which we have reason to believe may be more recent. Compare the almost black bones of the beaver, for instance, with the light brown bones of the otter in the two mounted skeletons in the Sedgwick Museum.

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