Like any modern science the science of Geology has Its own nomenclature and terminology. Since it is an interdisciplinary science it has taken to its bosom terms also derived from physical chemical and biological sciences relevant words from these also find a place, as also words from peripheral disciplines The aim of this work is to cover all essential terms used in different branches of the science and to provide concise but adequate definitions and information for each. Descriptions of only basic mineral groups and species are given for there are more than 3700 minerals known. Similarly, the number of rock types runs into hundreds, and only the main groups are defined. The Basic stratigraphic units, system/period and above, and their nomenclature, classification and ages, are however listed, and follow. The latest Indternational Stratigraphic Chart 2004 of the International Commission on Stratigraphy of the International Union of Geological Sciences. In addition, Some Stratigraphic unit names found in geological literature or proposed elsewhere have also been included.