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living. This small proportion (about 3 per cent.,) varies a 

 little, of course, with the deposites of different regions ; and the 

 deposites of this formation, like those of any other are charac- 

 terised less by the precise proportion of their extinct fossils, 

 than by possessing a number of shells peculiar to the particular 

 era, and found in no other tertiary groups. 

 Estuaries. Inlets of the land, which are entered both by rivers and 

 the tides of the sea. Thus we have the estuaries of the Thames, 

 Severn, Tay, &c. Etym. sestus, the tide. 



Fault, in the language of Miners, is the sudden interruption of the 

 continuity of strata in the same plane, accompanied by a crack 

 or fissure varying in width from a mere line to several feet, 

 which is generally filled with broken stone, clay, &c. 



Felspar. A simple mineral, which, next to quartz, constitutes the 

 chief material of rocks. The white angular portions in granite 

 are felspar. 



Ferruginous. Anything containing iron. Etym., ferrum iron. 



Formation. A group, whether of alluvial deposites, sedimentary 

 strata, or igneous rocks, referred to a common origin or period. 



Fossil. All minerals used to be called fossils, but geologists now 

 use the word only to express the remains of animals and plants 

 found buried in the earth. Etym., fossilis, anything that may 

 be dug out of the earth. 



Galena, a metallic ore, a compound of lead and sulphur. It has 

 often the high appearance of highly polished lead. Etym., 

 yaksu, galeo, to shine. 



Garnet. A simple mineral generally of a deep red colour, crystal- 

 lized, most commonly met with in mica slate, but also in granite 

 and other igneous rocks. 



Gault. A provincial name in the east of England for a series of 

 beds of clay and marl, the geological position of which is be- 

 tween the upper and lower greensand. 



Gneiss. A stratified primary rock, composed of the same materials 

 as granite, but having usually a larger proportion of mica, and 

 a laminated texture. The word is a German miner's term. 



Granite. An unstratified or igneous rock, generally found inferior 

 to or associated with the oldest of the stratified rocks, and 



