390 



Eocene. The strata deposited under the oldest of the tertiary epochs, 

 as, for example, ilie Paris f^asin. 



Estua ies. Inlets of sea into the land. The tides and fresh water 

 streams niititrlo and flow into ihem. They include not only the portion 

 of the sea adjacent to the mouths of rivers, but extend to the hmit of 

 tide water on these streams. 



Ext/vice. Ingt'oloijy, fossil remains. 



Fault. A dislocation of strata, at which the layers on one side of a 

 dyke or fissure have slidden past the corresponding ones on the other. 

 These dislocations are often accon)|)aijied by a dyke. They vary from 

 a few lines to several hundred feet. 



Fdtlspar. One of the simple minerals, and, next to quartz, one of 

 the most abundant in nature. 



Ferrwjmous. Containing iron. 



Fbiviatile. Beldrfjinj; to a river. 



Formation. A group of rocks which were formed during a partic- 

 ular pc^riod, or which aro referred to a common origin. 



Fostiils. The rt-mnins of animals and [)lants found buried in the 

 earih, or enclosed in rocks. Some of ihese are but slightly changed, 

 others are petiifie<l, and the organic replaced by mineral matter; some 

 have decayed and left the impression of the bodies, while others have 

 been formed by mineral matter deposited in the cavities left by the de- 

 cay of the organic body. These last are called casts. The term pe- 

 trifaction is applied to those cases in which organic matter has been re- 

 place<l by mineral substances. The form ami structure of the original 

 body both remain. In casts the exterior form alone is preserved. Fos- 

 sils are also called organic remains. 



Fossiliferous. Containing organic remains. 



Galena. An ore of lead composed of lead and sulphur. 



Garnet. A simple mineral, wliich is usually red and crystallized. It 

 is abundant in most jirimitive rocks. 



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

 as granite, but the mica is distributed in parallel layers, which give it a 

 striped aspect. 



Geiide. Geodl/eroiis. Geodes are small cavities in rock, generally 

 lined will] quarlz^se or calcareous crystals. 



Geology. A science which has for its object to investigate the struc- 



