Jurassic to Present Day

During the long time span, some 146 million years, since the deposition of the youngest Jurassic rocks in the area, (which was before the end of the Jurassic Period) we have little evidence of the geological history, which is very tantalising as it was in this time span that the landscape which we know today was formed.

It is thought that for much of the time the area was above sea level and so subjected to erosion. During the Cretaceous, sea level rose and a succession of clays, chalk and sands were deposited over much of what is now the British Isles, but whether the chalk ever covered the area of South Gloucestershire is open to debate. We do know that there were earth movements both during the Cretaceous and during the Paleogene and it may be these which controlled the pattern of drainage which developed.

The River Severn follows the line of an old fault, which was re-activated, and the drainage on all the older rocks follows a pattern, which is unrelated to the geological structure. It is assumed the drainage pattern was formed on a cover of rocks, possibly the Chalk, which have since been eroded away.

We know that a great deal of erosion has occurred to remove most of the Jurassic sandstones and limestones, which covered the older rocks. The fretted edge of the Cotswold scarp shows where even today, springs are causing erosion of the scarp edge.

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