474 [Assembly 
oxygen. It is incapable of supporting combustion, and deleterious 
to animal life. It is heavier than atmospheric air ; and hence is 
found at the bottom of wells, cisterns or caves. Its presence may 
alvsrays be known by letting down a candle, by which it will be ex- 
tinguished ; a precaution which should always be observed previous 
to descending into them. A person is rendered entirely incapable 
of exerting himself the moment he inhales this substance, and of 
course cannot extricate himself when immersed in it. 
Carboniferous. Coal-bearing. 
Chloride. A combination of chlorine and a base, as sodium, which, in 
chemical language, is called a chloride of sodium; in common lan- 
guage, it is dry sea salt. 
Chert. A silicious mineral resembling flint, hornstone, &c. Rocks 
containing it, are called cherty. 
Chlorite. A soft greenish mineral composed of minute scales closely 
compacted together. It differs very little from soapstone. Rocks 
containing it, are said to be chloritic. 
Clinkstone. A rock allied to basalt, which rings when struck. 
Cleavage, is the separation of the lamina of rocks or simple minerals 
in certain constant directions. In rocks, it is not always parallel to 
the planes of stratification ; and hence the planes of cleavage may 
be mistaken for those of stratification, and vice versa. 
Coal measures, coal formation. Rocks containg coal. 
Conformable. The arrangement of the strata of two rocks in parallel 
position. 
Conglomerate. Masses of rounded stone, gravel and dirt, cemented to- 
gether. 
Cretaceous. Belonging to the chalk formation. 
Crop out, and out crop. Emergence of a stratum or a rock from the 
soil, or from the adjacent strata or rocks ; in other words, its appear- 
ance at the surface. 
Crystal, crystalline. A geometrical solid ; the latter, an assemblage 
of imperfectly defined crystals. 
Crustacea. Animals having a thin coating or crust, like the lobster, 
which they shed periodically. 
Delta. Alluvial lands formed near the mouths of rivers, of a triangular 
shape, and included between the branches of the river and the sea- 
shore. Large rivers, just before their entrance into the sea, frequently 
divide into several branches ; this division is in consequence of the 
earthy matter borne down by the river to its junction with tide water, 
where it is deposited, forming thereby banks of sediment which rise 
in time above the water. 
Denudation. A term used to express the removal of sedimentary mat- 
ter from any area. Rocks from which any covering has been swept 
off by currents of water, are said to be denuded. Valleys are some- 
times formed in this way; they are then called valleys of denudation. 
Deoxidized. Deprived of oxygen. 
Dicotyledonous. One of the grand divisions of the vegetable kingdom, 
founded on the form and structure of the seed, which, as the name 
expresses, has two seed lobes. 
