Portsdown within the geology of the UK

Portsdown Hill lies along the northern edge of Portsmouth Harbour in the south of England, just east of Southampton. It is shown within the blue rectangle on the map below.

The Varied Geology of the UK

The map displayed is based on a geological map of Britain, but uses non-standard colours. Using shading, it indicates the different eras and ages of the sedimentary rock outcrops.
We are extraordinarily lucky within the UK to have outcrops of rocks from Pre-Cambrian age (in Wales and Scotland), through to the very recent beds of South-East England.
A huge amount of the Earth's history can thus be seen in the small area of our Island.

It was a canal-engineer, William Smith, who first noted the difference in the rock strata and fossils as his work took him across the country. From observation of how the rocks and the fossils within them changed, he produced the first geological map of the country. This was finally published in 1815, and the story of its creation can be read in Simon Winchester's "The Map That Changed the World".

The style of this first map - which now hangs in the UK Geological Society Headquarters in Burlington House, Piccadilly - has since been copied world-wide.

Green for the Cretaceous Chalk and yellow for the younger beds are his colours, the rest are my own.

The colour-coding of the map indicates the following:

Sedimentary, from youngest to oldest:

• Cenozoic outcrops in yellow, in the south and east of England
• Mesozoic outcrops, in green, getting darker with age
• Palaeozoic outcrops in brown, getting darker with age.
• Pre-Cambrian outcrops in black (outlined in dark yellow), in Longmynd, Wales, and north-west Scotland

Igneous and Metamorphic

• Igneous outcrops in red and dark-pink,
• Metamorphic outcrops in dark and light purple

Hampshire geology within the UK

Portsdown sits in southern Hampshire, where the rocks are all of Cretaceous and Cenozoic age - relatively young. The geology of Southern Hampshire is shown here, with Portsdown being the green outcrop of Chalk in the blue rectangle.

The green beds are all Cretaceous, with the Chalk shown in the brightest, lightest green. The other beds are Cretaceous clays (and other sediments), getting darker with increasing age.

The yellow beds are all Palaeogene, which is the oldest epoch of the Tertiary era. The shading follows my convention of darkness reflecting greater age.

To read more about the geological time units, please go to Geological Time.
Alternatively, return Home or go to the Site Map, or take a brief tour through time of the past 250 million years of the Earth's geographical framework.

return to top

For any comments, suggestions or contributions, please e-mail me at: portsdown@bbm.me.uk