Autograph letter signed from Decimus Burton to Sir Charles Lyell, dated 14 May 1814: "I have considered the subject put to me in your note. I take the superficies of London, Westminster[,] Southwark, Finsbury[,] Marylebone etc. to be 16 sq. miles. I suppose the cubical mass of stone, brick & paving stone over that area to be 74,000,000 cubic yards in the Houses, Churches, Public Buildings etc. Taking the number of Houses to be 250,000 – and this would give about 5 feet thickness or height of solid material over the 16 sq. miles. The above can but be considered as an approximation to the truth. In arriving at an average of the cubical content in each house. I give the small houses the benefit of the Churches & Public Buildings [...]".