126 NATURAL SCIENCE [February 



too strongly insisted upon. And he quotes Sir Douglas Galton to 

 the effect that builders often remove and sell the clean sand and 

 gravel, lilliug in the area thus cleared with all kinds of unnaraeable 

 tilth, and then proceed to run up houses into which emanations from 

 the rotting mixture underneath cannot fail to rise, and so produce the 

 sore throat and other diphtheritic symptoms so well known to many 

 dwellers in this great city. 



Natural soils are primarily derived from the true sub-soil, which 

 is itself the result of decomposition of the underlying rock. As a 

 rule, it is thin, but it may be 3 feet or more in thickness. A large 

 part of London must originally have been marsh land, but there are, 

 according to Mr Woodward, but few areas now existing in the heart 

 of London — these are Walbrook, Pimlico, Lambeth, Deptford, Eother- 

 hithe and the Isle of Dogs. It is not unusual at the present day for 

 the Thames to rise high enough to flood the lowest parts of Wapping, 

 Deptford, liotherhithe, Southwark and Lambeth. There is, moreover, 

 a protective covering of ' made ground ' on many of the old marsh- 

 lands, reaching even to 6 feet in some places at Pimlico. The Gros- 

 venor Hotel stands on 4 feet of 'made ground,' 11 feet of alluvium, 

 and 9 feet of sand and gravel. At the new Admiralty works, it may 

 have been observed, while the foundation operations were going on, 

 that it was necessary to pump out the old marsh and build what was 

 really a concrete box, so that the cellars and vaults of that structure 

 should possess the necessary dryness for the safe storage of records. 

 Many of these old marshy tracts have been utilised for the building 

 of docks, while others have served for factories, gas and soap works, 

 and other matters not requiring a great resident population. Mr F. 

 J. Bennett has pointed out that one of the chief objections to any 

 large population on marshy ground is the difficulty of introducing 

 any eifective system of house drainage, owing to the want of fall to 

 carr}' away the sewage. 



Tlie large gravel areas around London are not always healthy. 

 For instance, there may be a thin capping of gravel over a clay. 

 This, of course, would lead to there always being a certain amount of 

 water in the gravel, and so a dampness would be ever present, which 

 would penetrate the house. Taking in descending order the higher 

 txravels, Blackheath Beds, Bagshots, Thanet Sand, Greensands and 

 Hastings Beds, the various pros and cons for building are discussed by 

 Mr Woodward, and among other curious points he reminds us of a 

 note by the late Mr Topley to the effect, that some of the Hastings 

 Sandstones are so fine in grain as to hold up water almost as well as 

 a clay, thus showing how many points it is necessary to consider when 

 the choice of a site to live upon is important. 



Proceeding to discuss the Woolwich and Ptcading Beds, Brick- 

 earths, Clays-with-Flints, Boulder Clays, London Clay, Gault, and 

 Weald Clays, all of which mean dampness in some degree, and some 

 of which mean ruin in very dry seasons, as many found to their cost 

 in the dry summer of several years ago, Mr Woodward comes to the 

 Chalk. The Chalk seems to hold the palm for healthy and dry sites, 

 but of course one has to be wary of gravel pipes, and must not expect 

 to gain prizes at horticultural exhibitions, for the soil is as a rule poor, 

 and generally unsuitable for plantations in its natural state. 



