- As indicated s.v. "London," the levels of the City have varied considerably from time to time since its foundation, with the result that the present streets and buildings are at a much higher level than those of the ancient City. The subject is dealt with graphically in Plan 1, which shows the depth of the "made ground" in various localities and also the levels at which Roman remains of various kinds have been reached, so far as these have been ascertainable.The London Clay has been reached in Copthall Avenue at a depth of 18-24 feet, under St. Mary le Bow at about 20 ft., and at Bishopsgate at about 30 ft., while the gravel has been reached at depths varying from 10 ft. at Beer Lane to 22 ft. at London Wall, and 30 ft. in Blomfield Street.The marsh from the river's edge extends to about 300 ft. inland, the ground shelving upwards towards Thames Street.Black boggy soil with indurated bog earth and peat have been found at different points in the area extending from Princes Street, Lothbury and Throgmorton Street to London Wall, and from Finsbury Pavement to Blomfield Street and New Broad Street.It may be interesting to indicate the depths to which the "made ground" extends in different localities.In the western area of the City the depth extends in Chancery Lane (Holborn end) to 12-14 ft.; Holborn Bars, to 13 ft.; Bartlett's Buildings, 7 ft.; Leather Lane, 10 ft.; Newgate Street, 11 ft.; Warwick Square, 18 ft.; New Bridge Street, 25 ft.; Blackfriars (Apothecaries' Hall), 12-121/2 ft. Old Fish Street, 10 ft.; Godliman Street, 71/2 ft.In the Central area : Lombard Street, to 14 ft.; Bank of England, 22 ft.; Gracechurch Street, 16 ft.; Warnford Court, 221/2 ft.; Cannon Street, 9 ft.; King William Street, 11 ft.; Rood Lane, 15 ft.; Billingsgate, 27-35 ft.In the eastern area : Gravel Lane, Houndsditch, to 184 ft.; Minories, 15 ft.; Royal Mint, 11 ft.; Royal Mint Street, 17 ft.; Tower Hill at Gt. Tower Street, 51/2 ft.; Tower Hill at the western entrance to the Tower, 14-22 ft.In the northern area : Jewin Crescent, to 23 ft.; Finsbury Pavement, 10-16 ft.; London Wall, 91/2-12 ft.; Moorgate Street, 17-18 ft.; Bishopsgate, 7 ft.It will thus be seen that the depth varies from 7 to 35 feet over the entire area.
A Dictionary of London. Henry A Harben. 1918.