GLOSSARY. 
Eocene. The strata deposited during the oldest of the tertiary 
epochs, as, for example, the Paris Basin. 
Estuaries. Inlets of the sea into the land. The tides and fresh- 
water streams mingle and flow into them. They include not 
only the portion of the sea adjacent to the mouths of rivers, but 
extend to the limit of tide-water on these streams. 
Exuvia. In geology, fossil remains. 
F. 
Fault. A dislocation of strata, at which the layers on one side 
of a dike or fissure have slidden past the corresponding ones on 
the other. These dislocations are often accompanied by a dike. 
They vary from a few lines to several hundred feet. 
Feldspar. One of the simple minerals, and, next to quartz, one 
of the most abundant in nature. 
Ferruginous. Containing iron. 
Fluviatile. Belonging to a river. 
Formation. A group of rocks which were formed during a 
particular period, or which are referred to a common origin. 
Fossils. The remains of animals and plants found buried in 
the earth or enclosed in rocks. Some of these are but slightly 
changed, others are petrified, 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 decay of the organic body. These last 
are called casts. The term petrifaction is applied to those causes 
in which organic matter has been replaced by mineral substances. 
The form and structure of the original body both remain. In 
casts the exterior form alone is preserved. Fossils are also called 
X)rganic remains. 
Fossiiiferous. Contaming organic remains. 
G. 
Galena. An ore of lead, composed of lead and sulphur. 
Garnet. A simple mineral, which is usually red and crystal- 
lized. It is abundant in most primitive rocks. 
Gneiss. A stratified primary rock, composed of the same ma- 
terials as granite, but the mica is distributed in parallel layers, 
which give it a striped aspect. 
Geology. A science which has for its object to investigate the 
structure of the earth, the materials of which it is composed, the 
manner in which these are arranged with regard to each other; 
and it considers the action of all natural causes in producing 
changes, such as the effects of frost, rain, floods, tides, currents, 
winds, earthquakes, and volcanoes. 
Economical Geology refers to the application of geological facts 
and -observations to the useful piirposes of civilized lifie. 
