Holmesdale Natural History Club. 31 



in the mud itself. The composition of this mud will vary in different part& 

 of the river. In its upper reachss, where the stream flows through an 

 agricultural district, the deposit will consist of sand, clay, and the debris of 

 growing crops and decaying leaves and manure, with some of the contents 

 of ponds, ditches, and streams by which these other matters are conveyed to 

 the river. In the thickly peopled districts, as from London to "Woolwich, 

 and at the outfalls of the London sewers, there will be added to the former 

 deposit the contents of house-drains and sewers, the rubbish of dust-bins, 

 and the refuse of factories, with road grit and gutter mud. Still lower 

 down, as we approach the estuary of the river, the flood tide will bring in 

 its contribution, sand and mud from the sea, with seaweed and other 

 organisms, and the ebb tide will make a still larger addition of mud and 

 other matters washed out from the saltings which border the estuary and 

 lower reaches of the river. The different matters from these and other 

 sources thus brought into the river are subjected to a variety of influences, 

 and undergo a variety of changes. Salt water and fresh water, and organic 

 bodies belonging to each of them, with every variety of town refuse, are all 

 more or less mixed together, and in this mixed state are subjected to a variety 

 of movements produced by the flux and efflux of the tide, the disturbance pro- 

 duced by winds, and by the traffic of steam and other vessels on the river. 

 With such a variety of elements at work, it is little to be 

 wondered that there should be great difEerence of opinion on many points 

 connected with the physical history of the river. On one of these points, 

 as you are doubtless aware, the Conservators of the Thames and the 

 Metropolitan Board of Works have for some time past kept up an earnest, 

 not to say acrimonious contest, the Conservators having asserted that mud 

 banks are forming in the river, and that these mud banks owe their origin 

 to the discharge of matters from the outlets of the London sewers at 

 Barking Creek and Crossness. One of the mud banks in dispute is opposite 

 St. Thomas's Hospital, and of comse if it can be proved that this and similar 

 banks are formed in the way the Thames Conservators believe they are, it 

 follows that London is still on the banks of a river largely contaminated 

 with sewage, and that the great expense incurred in removing the outlet of 

 its sewers to Crossness and Barking will be of little avail in a sanitary 

 point of view. It becomes, then, a matter of great importance to determine 

 whether the flood tide has the power of transporting matters from the lower 

 to the higher reaches of the river, and also wiiether we have any means by 

 which we can determine whence the matter composing any particular mud 

 bank has been derived. On both these points I have thought that an 

 investigation of the animal and vegetable organisms found as a constituent 

 part of the mud at any particular locality might afford useful if not decisive 

 information. With a view of testing this principle I have obtained mud 

 from different parts of the river, commencing half a mile above Teddmgton 

 Lock, and ending with the estuary or mouth of the river at Sheerness. 

 From every one of the samples I have collected as many Diatoms as I pos- 

 sibly could, and tabulated the result. I have selected the Diatomacere as a 



