GLOSSARY OF TECHNICAL TERMS. 
Alluvium. A recent deposit of earth, sand, gravel, peat, &;c. ; the term 
is apphed to depositions which are now accumulating, as at the 
mouths of rivers, &;c. 
Alum rocks. Rocks which, by decomposition, form alum. 
Amorphous. Bodies devoid of a regular form. 
Amygdaloid. A rock more or less cellular in its structure, and at the 
same time abounding in cavities in the shape of an almond. It is 
one of the class usually called Trap rocks. 
Anticlinal axis, ridge, ^c. Tlie line from which the strata of any for- 
mation dip in two directions, like the roof of a house. 
Augite. A simple mineral of variable colours, passing from white 
through gray, green and black of different shades. It is a constituent 
of many volcanic and trappean rocks, limestone, granite, &c. 
Basalt. A black or grayish black compact rock occuring frequently 
in a columnar form, as at the Giant's Causeway in Ireland. Many 
geologists consider it to have been formed by the fusion of augitic 
and feldspathic rocks under great pressure, as at the bottom of an 
ocean or deep sea ; hence its compact structure. 
Basin. Deposits lying in a hollow or trough-shaped excavation, are said 
to occupy basins. 
Bed. A mass of mineral matter lying between the layers or strata of 
any rock. 
Bitumen, bituminous, <^c. An inflammable substance which presents 
itself under two forms, a solid and liquid ; when in the former state, 
it is called asphaltum. In its liquid state it is like tar. Seneca oil 
is an example of it. Coals, slates, limestones are often bituminous. 
Blende. A German name for sulphuret of zinc. 
Boulders. Rocks which have been transported some distance from their 
original beds ; they are more or less rounded by attrition and the ac- 
tion of the weather. 
Botryoidal. Resembling in form a bunch of grapes. 
Breccia. A rock or portion of a rock composed of angular fragments, 
cemented together by lime, iron, or some other substance. 
Calcareous spar is crystallized carbonate of lime. 
Calc sinter. A deposition of porous carbonate of lime, from the waters 
of mineral springs. 
Carbon. A simple substance, known in a pure state in the diamond 
only. It is one of the combustible elements in coal. 
Calciferous. Bearing or containing lime. 
Carbonates. Compounds formed by the union of carbonic acid and a 
base. 
Carbonic acid. An acid gaseous compound composed of carbon and 
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