I J K

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 56 million years from 201 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.