Wales is a peninsula in the south-west of the island of Great Britain. The entire area of Wales is about 20,779 km² (8,023 square miles). It is about 274 km (170 miles) north-south and 97 km (60 miles) east-west. Wales is bordered by England to the east and by sea in the other three directions: the Welsh Channel to the south, St George's Channel to the west, and the Irish Sea to the north. Together, Wales has over 1,200km (750 miles) of coastline. There are several islands off the Welsh mainland, the largest being Ynys Môn (Anglesey) in the north west.
Wales is mountainous, particularly in the north and central regions. The mountains were shaped during the last ice age, the Devensian glaciation. The highest mountains in Wales are in Snowdonia (Eryri), and include Snowdon (Yr Wyddfa), which, at 1085 m (3,560 ft) is the highest peak in Wales. The Brecon Beacons (Bannau Brycheiniog) are in the south and are joined by the Cambrian Mountains in mid-Wales, the latter name being given to the earliest geological period of the Paleozoic era, the Cambrian.
In the mid-nineteenth century, two prominent geologists, Roderick Murchison and Adam Sedgwick used their studies of the geology of Wales to establish certain principles of stratigraphy and palaeontology. After much dispute, the next two periods of the Paleozoic era, the Ordovician and Silurian, were named after ancient Celtic tribes from this area.

Regions of Wales

Snowdonia National Park Authority
Official site of the Brecon Beacons National Park Authority
The Gower Information Center: Broad Pool
Ogg, James. GSSP for the Base of Telychian. Retrieved on 2006-07-01.
Ogg, James. GSSP for the Base of Aeronian. Retrieved on 2006-07-01.
John L. Morton, King of Siluria — How Roderick Murchison Changed the Face of Geology (Brocken Spectre Publishing, 2004, ISBN 0-9546829-0-4)
This article incorporates text from the Encyclopædia Britannica Eleventh Edition, a publication now in the public domain.
Martin J. S. Rudwick, The Great Devonian Controversy: The Shaping of Scientific Knowledge among Gentlemanly Specialists (University of Chicago Press, 1985) — the rise of Murchison to power
James A. Secord, Controversy in Victorian Geology: The Cambrian-Silurian Dispute (Princeton University Press, 1986) — documents the battle between Murchison and Adam Sedgwick