The layers that compose the southeastern half of England slope generally down southeastward. This broad fact was discovered in the 1790s by a humble genius, William Smith.

(William Smith is the subject of Simon Winchester's The Map that Changed the World, 2001, a popular though imperfect book. I call it imperfect because Winchester doesn't seem to imagine the extent of the labour that Smith must have put in, riding along most of the roads of England and Wales and probing their banks, to plot the boundaries on his map between rocks of different ages.)

When I was about thirteen I read somewhere an enlightening explanation of the structure of England's southeastern toe. Three layers that were laid down flat in seas of the Cretaceous era (146 to 65 million years ago) were later buckled gently up into a kind of long dome, called an anticline. Their upper parts were (even as they were rising) removed by erosion. The result is a concentric arrangement. In the middle is the low dome of the Weald; around it, an incomplete ring of inward-facing scarps, made of the layer called greensand, and including Leith Hill; outermost, the wider band of the chalk, forming the inward-facing scarps of the North Downs and South Downs. (Clays of later ages filled the hollows between and around these formations.)

PICTURE: geolDowns

Later, I learned that all this is only a wrinkle in a wider pattern.

Cretaceous band across England

Jurassic (and Triassic and Cretaceous

The thick layers of the Jurassic age, forming a diagonal band across England, come to their end along this coast. As they crumble into the sea, they release the fossils for which the coast is famous, especially in the stretch to the east of Lyme. The stretch to the west is even more remarkable.

Looking at the British Isles from higher up (as it were) you can see that, over geological time—a few million years—they are a diminishing rag of land off the edge of Europe, in process of crumbling into the sea, like a sand-castle as the tide comes in.

from northeast:

Jurassic: Yorkshire Moors and Cleveland, Lincoln Edge,  . . .  Cotswolds,

separating: Vale of Pickering . . . 

Cretaceous: Flamborough Head, Yorkshire Wolds, Lincoln Wolds,  . . .  Chilterns,