Glossary of geological terms
ABCDEFGHI J KL
MN OP QRSTU VW X Y Z
I
Iapetus / Iapetws
An ocean which in Cambrian and Ordovician times lay between the former continents of Laurussia and Avalonia. Its eventual closure during the Silurian period led to the mountain-building event known as the ‘Caledonian Orogeny’. The name derives from the figure who in classical times was the father of ‘Atlantis’.
Interstadial / Rhyng-gyfnod cynhesol
A length of time within an ice age when warmer conditions persisted. The colder periods are known as ‘stadials’.
Irfon Formation / Ffurfiant Irfon
A succession of mudstones and siltstones laid down during the Ludlow epoch of the Silurian period.
J
Jurassic / Jwrasig
Geological period which lasted 54 million years from 199 to 145 million years ago. See geological timescale.
K
Karst / Carst
A landscape containing a range of features typical of those developed over limestone such as rock pavements, sinkholes, caves and resurgences. Named after type area in former Yugoslavia.
Kettlehole / Pant ia llonydd
A depression in the ground surface left by the melting of an ice mass buried under moraine. It may be dry, boggy or contain a pool or lake.