Acotyledonous. Plants having no seed-lobes. Mosses and ferns belong to this division, and most of the coal plants are acotyledonous.
Actynolite. A green mineral found chiefly in primitive formations often crystallized in six sided prisms.
Aerolites. Stones which appear to have fallen from the higher parts of the atmosphere. They are sometimes called Meteorites.
Algæ. A division of plants including the common sea-weeds.
Aluminous. Containing alumina, or rather silicate of alumina, which is the base of pure clay. Thus, aluminous means clayey. The word is, however, sometimes used in the sense of containing alum, a sulphate of alumina and potash.
Ammonite. A fossil genus of many-chambered shells allied to the Nautilus, named from their resemblance to the horns on the statues of Jupiter Ammon.
Amorphous. Without regular form.
Amorphozoa. Animals without definite form—sponges.
Amygdaloid. Almond-shaped. Any rock is called by this name which contains rounded or elongated minerals imbedded in some simple mineral or base.
Amygdaloidal (in mineralogy). A conglomerate.