Geology Site Account

Site name: College Wood Gravel Pits, Blackmore

Grid reference: TL 623015

Brief description of site:

College Wood, a large, ancient wood near Blackmore, contains a number of overgrown and disused gravel pits. The origin of this gravel, known as Stanmore Gravel, is unclear. It dates from the early part of the Ice Age and may have been deposited by northward-flowing tributaries of the pre-diversion Thames, or it may be of marine origin. Exposures of this gravel therefore have the potential for future research. The pits are situated in private woodland with no public access.

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Summary of geological interest

The sand and gravel exposed in the College Wood pits is referred to on geological maps as Stanmore Gravel and it occurs elsewhere on the high ground of Brentwood district. How it was formed has been debated by geologists since the 19th century. Its origin is still unclear today although one theory is that it was laid down by a river, probably over one million years ago, during the early part of the Ice Age. This was at a time when the Thames flowed across what is now North Essex and Suffolk. The river in question may therefore have been a northward-flowing tributary of the Thames. See Ellison (2004) for a discussion about the origin of this deposit.

The gravel in College Wood contains vein quartz, quartzite and rare Lower Greensand pebbles. The gravel outcrops here and in nearby Parsons Spring (in Chelmsford District) are similar and are characterized by rather different pebble assemblages compared to occurrences elsewhere in the area (Millward et al 1987). Future research here may therefore be important in helping to establish an origin for this enigmatic deposit.

The geological survey memoir for the Epping District (Millward et al 1987) calls this gravel Older Head. The British Geological Surveys picture library contains an image of the gravel in one of these pits at TL 6236 0169.

Gravel-pit in College Wood near Blackmore. Cryoturbated, rather clayey sand and gravel. The white angular pebbles are patinated flint. The well-rounded pebbles consist mostly of flint but some vein quartz. Photo © British Geological Survey (P212163).