Geology Site Account

Historical site only

In 1868 the Gas Light and Coke Company began work on a giant gas works on low-lying marshland south of Barking. From the 1870s onwards this gas works supplied the whole of London with gas and the site and surrounding area was named Beckton after Simon Adams Beck, the manager of the company. With the rapid expansion of London it grew to become Europes largest gas works which incorporated a Tar and Liquor Works where by-products of the gas works coal were produced. Like other industries at the time, the works obtained its water supply from deep wells or boreholes, and by 1913 they were 12 wells here. One of these, sunk in 1910 and known as borehole No. 4, proved to be of great geological interest as it was one of the few wells in the London basin to penetrate the ancient basement rocks which are present in this area at a depth of some 300 metres (almost 1,000 feet).

Old well records give details of each stratum of rock that was encountered, each one identified by its unique character or from the fossils it contained. No. 4 borehole passed through London Clay, Woolwich & Reading Beds and Thanet Sand, entering the Chalk at a depth of 39 metres (128 feet). The Chalk beneath Beckton was found to be 197 metres (647 feet) thick and water from the Chalk aquifer entered the borehole and rose to within only a few metres of the surface. However, a decision to deepen the borehole was made in the hope of an even greater supply of water and drilling continued beneath the Chalk through 61 metres (200 feet) of Upper Greensand and Gault.

Up to this point all of the rocks through which the bore had penetrated were relatively undisturbed, horizontal strata and of increasing geological age with depth. The Gault, a marly clay of Cretaceous age (about 100 million years old) contains marine fossils and the borehole record tells us that the last section of core brought up from the base of the Gault contained an ammonite. However, the next rock encountered - the Palaeozoic basement - was different to the Gault in every way and represented a far more ancient period of geological time. Consisting of hard green and red sandstones and siltstones inclined at an angle of 45û, these rocks are known as Old Red Sandstone and fossil plant remains recovered from the borehole indicate that they were deposited during the early Devonian period about 400 million years ago. This was a time when animals were just beginning to colonise the land and what is now England was situated south of the equator. The sediments laid down at that time have been turned to rock, steeply inclined by mountain-building episodes, uplifted, and then eroded by the elements over millions of years.

The junction between these basement rocks and the overlying Gault is an example of what geologists call an unconformity, where a sequence of rocks is missing. In this part of London almost 300 million years of geological history is absent from the rock record between the Devonian period and Cretaceous period when the sea finally flooded in to deposit the Gault. This junction is therefore an ancient land surface which was in existence throughout much of the Jurassic and early Cretaceous periods when the climate was tropical and dinosaurs were the dominant creatures. This land surface is now 300 metres (almost 1,000 feet) below the surface at Beckton.

The decision to continue the borehole into the basement rocks was rewarded by the water level rising further, filling the entire borehole and overflowing at the surface creating an artesian well. Such was the supply of water from this well that a rate of 1,000 gallons an hour was recorded in July 1911. The temperature of the deep water was found to be 10 degrees warmer than that obtained from the Chalk which would be expected from the geothermal heat present in rocks at depth.

Beckton Gas Works closed in 1967 as a result of competition from cheaper North Sea Gas. The area has now been redeveloped and the precise position of No. 4 borehole is on the front lawn of the NHS Tollgate Health Centre in Tollgate Road. There is the opportunity here for a small plaque or possibly an information board on the borehole to tell the public what has been learnt about the buried landscape beneath East London during a mind-bogglingly distant period of the Earths history.