+--------------------------------------------+ | On a Central Line in the | | Tertiary District. | +--------------------------------+-----+-----+ | |Sand.|Clay.| | +-----+-----+ | Sand.Clay.| ft.| ft.| | ft. ft. | | | |London: | | | | Millbank 49 40} | | | | Trafalgar Square 49 30} | | | | Tottenham Court Road 35 30} | | | | Pentonville 34 44} | 46 | 39 | | Barclay's Brewery 55 42} | | | | Lombard Street 53 35} | | | | The Mint 49 38} | | | | Whitechapel 45 50} | | | |Garrett, near Wandsworth | 20 | 52 | |Isleworth | 17 | 70 | |Twickenham | 7 | 50 | |Chobham | 3 | 45 | | +-----+-----+ | Average | 18 | 51 | +--------------------------------+-----+-----+ +--------------------------------------------+ | On or near the Northern Boundary | | of the Tertiary District | +--------------------------------+-----+-----+ | |Sand.|Clay.| | +-----+-----+ | | ft.| ft.| |Hatfield | 23 | 2 | |Watford | 25 | 10 | |Pinner | 12 | 32 | |Oak End, Chalfont St. Giles | 3 | 40 | |Hedgerley, near Slough | 5 | 45 | |Starveall, " " | 13 | 20 | |Twyford | 5 | 60 | |Sonning, near Reading | 12 | 54 | |Reading | 16 | 33 | |Newbury | 20 | 36 | |Pebble Hill | 9 | 39 | | | | | | | | | | +-----+-----+ | Average | 13 | 34 | +--------------------------------+-----+-----+ The average total thickness of the eastern district deduced from the nine sections we have taken gives 68 feet, of which 53 feet are sands and 15 feet clays. The larger area, 1849 square miles, over which the eastern portion of the Tertiary series extends, and the greater volume of the water-bearing beds, constitute important differences in favour of this district; and if there had been no geological disturbances to interfere with the continuous character of the strata, we might have looked to this quarter for a large supply of water to the Artesian wells of London. [Illustration: A Geological Section. Fig. 10.]