Constituents of Thames Mud. By Lionel S. Beale. 13 



water, and the remaining 45 are fresh-water species. As would 

 be supposed, some of the marine species are carried up the 

 river, and the fresh- water species downwards towards the sea. 

 Mr. Eoper found marine species at Hammersmith, but very few 

 fresh-water species were met with as low as Glravesend. " At 

 Gravesend, out of 47 specimens 8 only are decidedly peculiar to 

 fresh water, whilst at Hammersmith we find there are 29 fresh- 

 water species out of a total of 43, showing however that the 

 influence of the flood tide, even at that distance from the sea, gives 

 a decided character to the diatomaceae deposited by the water." 



Of the diatoms met with in Thames mud, some are found in a 

 living state, but the majority are not only dead but they do not 

 belong to the particular locality where their remains have been dis- 

 covered. The silicious shells or valves of these organisms are very 

 light and are often transported long distances. Suspended in 

 the moving water, many pass up and down the river and probably 

 form a part now of this bank, now of that. By this continual 

 movement, and by rubbing against sharp particles of sand and by 

 being buried in it, and then again disturbed, such delicate structures 

 necessarily become disintegrated, and are at last broken into those 

 very minute silicious fragments which exist in great numbers in 

 the mud of all the mud -banks examined. 



Mud-banks, especially on the surface, are in a state of constant 

 change. Formation and destruction, accretion and disintegration 

 are continual, and, when the facts are considered, one cannot feel 

 surprised that organisms which are formed high up or low down 

 the river, or at least parts of them, should eventually be discovered 

 in a resting place at a long distance from the seat of their deve- 

 lopment. Bodies formed high up the stream may be deposited at 

 its mouth, and those which inhabit the sea or brackish water may 

 be carried far up into the region traversed by and exposed to the 

 action of fresh water only. In fact, the ascent and descent of 

 light particles is clearly shown by the distribution of the diatoms 

 on the banks in difierent parts of the river, and this fact alone 

 would render it certain that many of the constituents of sewage 

 would in like manner be carried up and down bv the tide, and that 

 some would be found a long way from the point where they first 

 entered the Thames. 



Bacteria. 



are found in immense numbers in all the muds I have examined, 

 and exist in multitudes in Thames water, and in connection with 

 all the particles of organic matter held in suspension in the water, 

 or which have subsided to the bottom, or have fallen on the leaves 

 of plants or other objects which have prevented their further sub- 

 sidence. Bacteria are so very minute that they may easily be 



