Geology Site Account

Historical site only. Railway cutting which revealed Red Crag beneath gravel when it was constructed in the 19th century.

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Details

When the Manningtree to Harwich railway was constructed in the 1850s the cutting east of Wrabness station revealed Red Crag beneath gravel. This patch, or outlier, of Red Crag caps the high ground here and probably extends beneath the gravel almost as far as the cliff on the River Stour at TM 172 323.

The existence of Red Crag here would account for the occasional occurrence of Red Crag fossils on the beach such as whale bones and sharks teeth. The cutting again revealed Red Crag in 1875 when the line was widened and at that time it was reported to consist of four feet of laminated ironstone with a pebble bed of phosphatic nodules at the base, which was resting on London Clay bedrock. In north Essex and Suffolk the basal pebble bed of the Red Crag, or coprolite bed as it was called, was used as a raw material for the manufacture of phosphate fertiliser before the advent of artificial fertilisers. It has been recorded that about 1,000 tons of phosphatic nodules were obtained from Wrabness cutting and glebe for this important industry.

The Red Crag Sea existed about 2 million years ago and the outlier at Wrabness is one of the few surviving fragments of a once continuous deposit of Red Crag across north Essex that has been almost entirely destroyed by erosion. The most famous exposure is at Walton but other outliers are to be found at Beaumont and Little Oakley.

The gravel overlying the Red Crag at Wrabness is known as Ardleigh Gravel and was laid down during the Ice Age by the Thames when it flowed across East Anglia, probably about 700,000 years ago.