Underhill is the name given to the area of very steep land, at the northern end of the

Isle of Portland An isle is an island, land surrounded by water. The term is very common in British English. However, there is no clear agreement on what makes an island an isle or its difference, so they are considered synonyms. Isle may refer to: Geography * Is ...

Dorset Dorset ( ; archaically: Dorsetshire , ) is a county in South West England on the English Channel coast. The ceremonial county comprises the unitary authority areas of Bournemouth, Christchurch and Poole and Dorset (unitary authority), Dors ...

England England is a country that is part of the United Kingdom. It shares land borders with Wales to its west and Scotland to its north. The Irish Sea lies northwest and the Celtic Sea to the southwest. It is separated from continental Europe b ...

, which contains the villages of

Chiswell Chiswell , sometimes , is a small village at the southern end of Chesil Beach, in Underhill, Dorset, Underhill, on the Isle of Portland in Dorset. It is the oldest settlement on the island, having formerly been known as Chesilton. The small bay ...

, Castletown and

Fortuneswell Fortuneswell is a village in Underhill, Dorset, Underhill on the Isle of Portland, in Dorset, England. It lies on steeply sloping land on the northern edge of the island, known as Underhill, where Chesil Beach connects the island to the mainland. ...

. The remaining part of the island is known as

Tophill Tophill is a gently sloping area of land on the Isle of Portland in Dorset, England, rising from sea level at Portland Bill to near HMP The Verne at its northern end. On Tophill are five of the settlements on the island: Easton, Weston, ...

. The geology of Underhill is different from Tophill; Underhill lies on a steep

escarpment An escarpment is a steep slope or long cliff that forms as a result of faulting or erosion and separates two relatively level areas having different elevations. The terms ''scarp'' and ''scarp face'' are often used interchangeably with ''escar ...

composed of Portland Sand, lying above a thicker layer of

Kimmeridge Clay The Kimmeridge Clay is a sedimentary deposit of fossiliferous marine clay which is of Late Jurassic to lowermost Cretaceous age and occurs in southern and eastern England and in the North Sea. This rock formation is the major source rock for North ...

, which extends to

Chesil Beach Chesil Beach (also known as Chesil Bank) in Dorset, England is one of three major shingle beach structures in Britain.A. P. Carr and M. W. L. Blackley, "Investigations Bearing on the Age and Development of Chesil Beach, Dorset, and the Associat ...

and

Portland Harbour Portland Harbour is located beside the Isle of Portland, Dorset, on the south coast of England. Construction of the harbour began in 1849; when completed in 1872, its surface area made it the largest man-made harbour in the world, and rema ...

. This Kimmeridge Clay has resulted in a series of landslides, forming West Weares and East Weares.

References

Isle of Portland {{Dorset-geo-stub