The Rock of Gibraltar is composed primarily of limestone. The limestone in the Rock of Gibraltar consists of greyish-white or pale-gray compact. It sometimes becomes a finely formed crystalline. The crystalline may then come to exist as medium to thick bedded limestones and/or dolomites that locally contain chert seams.

The formations just noted comprise about three quarters of the Rock of Gibraltar. Geologists have found various poorly preserved, badly eroded, and rolled marine fossils within the Rock of Gibraltar. The fossils in the limestone in Gibraltar include various brachiopods, corals, echinoid fragments, gastropods, pelecypods, and stromatolites.

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