Geological Glossary

• Paleozoic - An era of geologic time that spans the time period 543 to 248 million years ago. It includes the Cambrian, Ordovician, Silurian, Devonian, Mississippian, Pennsylvanian, and Permian periods and is characterized by the appearance of marine invertebrates, primitive fishes, land plants, and primitive reptiles.
• Trias - The formation situated between the Permian and Lias, and so named by the Germans, because consisting of three series of strata, which are called in German the Bunter sandstein, Muschelkalk, and Keuper.
• Millstone Grit - a series of interbedded sandstones and shales that were deposited during the early part of the Upper Carboniferous.
• Sandstone - A sedimentary rock formed by the consolidation and compaction of sand and held together by a natural cement, such as silica.
• Shale - a sedimentary rock formed by the deposition of successive layers of clay.
• Marl - A crumbly mixture of clays, calcium and magnesium carbonates, and remnants of shells that is sometimes found under desert sands and used as fertilizer for lime-deficient soils.
• Quartz - a hard glossy mineral consisting of silicon dioxide in crystal form; present in most rocks (especially sandstone and granite); yellow sand is quartz with iron oxide impurities.
• Friable - Readily crumbled; brittle.
• Limestone - a sedimentary rock consisting mainly of calcium that was deposited by the remains of marine animals.
• Oolite - A small round calcareous grain found in limestones
• Galena - soft blue-gray mineral; lead sulfide; a major source of lead.
• Crinoid (Crinodial) - primitive echinoderms having five or more feathery arms radiating from a central disk.
• Ossicle - a small bone.
• Stratigraphy - The study of rock strata, especially the distribution, deposition, and age of sedimentary rocks.
• Petrology - The branch of geology that deals with the origin, composition, structure, and alteration of rocks.
• Ochre - Any of several earthy mineral oxides of iron occurring in yellow, brown, or red and used as pigments.

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