| ICE | A mineral, H2O, which may form speleothems in ice caves as, stalactite, stalagmite, drapery, crust, flower, flowstone, helictites and euhedral (having well formed crystal faces) crystals. Mineral, Rock and Chemical terms. Ref HF |
| ICE CAVE | (1) An otherwise normal cave with permanent (ie perennial) ice in it. (2) A cave that only has ice in it on a seasonal basis. Note: A cave entirely in ice, or under an ice sheet, is called a Glacier cave. Cave - Kinds of. Ref JJ |
| INDURATED | Soils and sedimentary rocks which have become hardened or cemented. Geology. Ref KG |
| INFLOW CAVE | A cave into which a stream enters or is known to have entered formerly. The stream cannot be followed downstream to the surface. Cave - Kinds of. Ref JJ |
| INFLUX CAVE | A cave entrance that has a stream flowing into it. cf Efflux cave. See also Inflow & Outflow caves. Cave - Kinds of. Ref MM |
| INORGANIC | Of non-biological origin. Biology - Flora & Fauna. Ref MM |
| INTERSTITIAL MEDIUM | The spaces between grains of sand, fine gravel or detritus filled with air or water which contains phreatobia. Speleology term. Ref JJ |
| INVERTEBRATE | An animal without a backbone. eg Annelid (worm), Mollusc (snail) & Arthropods. The main life forms found in caves. Fauna. Ref AC |
| INVERTED SIPHON | A siphon of U-profile. Cave - Parts of. Ref JJ |
| ISOPOD | An animal of the order of Crustaceans having 7 pairs of legs. Includes slaters. Commonly found in caves. Fauna. Ref MM |