Downland

The chalk is classified as a biomicrite,[3] with microscopic coccoliths and other fine-grained fossil debris in a matrix of micrite mud.

Since its deposition, the chalk in southern England has been uplifted, faulted, fractured and folded by the distant effects of the Alpine Orogeny.

[4] Sedimentary basins formed by rifting during the Triassic to Early Cretaceous were inverted during the Late Paleogene to Miocene leading to the formation of structures such as the Wealden Anticline and the Portland-Wight Monocline.

These periglacial effects included significant amounts of dissolution of the chalk and the modification of existing valleys due to a combination of frozen ground and snowmelt.

This is largely because of the purity of the chalk, which is about 98% calcium carbonate, and the consequent absence of soil-building clay minerals which are abundant, for example, in valley floors.

Steep slopes on chalk downland develop a ribbed pattern of grass covered horizontal steps a foot or two high.

The dominant habitat in chalk downland is typically calcareous grassland, formed by grazing from both livestock and wild animals.

Chalk downland is often unsuitable for intensive agriculture, horticulture, or development because of the nutrient-poor, shallow soil and difficult slopes.

The UK cover of lowland calcareous grassland has suffered a sharp decline in extent since the middle of the twentieth century.