Geology Site Account

Summary

The temporary geological exposures created when Harlow was built provided information on the geological history of the area. Further excavations in the vicinity could yield further information. (Note: the grid reference given is a general one for Harlow town)

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Site description (general)

The creation of Harlow New Town in the 1950s involved excavations in the sands, gravels and clays that were laid down during the Ice Age. Many fossils were found, the majority of which were from the boulder clay or till which was deposited by an ice sheet 450,000 years ago. A number of the fossils were of Jurassic Age, a fine example of which was a large ammonite found when constructing the artificial ski slope, formerly on Fifth Avenue.

In Harlow, the sequence of Ice Age deposits is comparatively complex. Boreholes and surface mapping have revealed that over much of the town there are two layers of gravel, separated by and overlain by boulder clay. The upper boulder clay caps much of the high ground of the New Town and the lower boulder clay crops out along the river valleys. The two clays differ in their constituents, which has led geologists to suggest that they are of different ages, perhaps even deposited by different ice sheets. It is now thought that the two are indistinguishable, the different character being due to the chalk fragments in the lower clay being dissolved by groundwater. All the boulder clay in Harlow is now accepted as part of the main sheet of chalky boulder clay; in most parts of Essex it is a single unit but in Harlow it contains beds of glacial sand and gravel, probably laid down in front of the advancing ice sheet.

Fossils from the excavations are in the collections of Harlow Museum and were originally on display to the public when the museum was situated in Passmores House on Third Avenue. Regrettably, since the move of the museum to new premises at Muskham Road the decision was taken to concentrate on human history and wildlife and no specimens relating to the geological heritage of the town are now on display.