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[ ASSEMBL Y 
to which it belongs; or it is a term applied to a mass which appears as 
if it was detached from the general formation, as its outcrop is at a 
distance from it. 
Oxide. The combination of a metal, or any substance with oxygen, 
which is not acid. 
Oxygen. One of the constituent elements of the air and water; that 
portion of the air which supports life and combustion. 
Fachydermata. An order of animals with thick skins, as the hog, ele- 
phant, rhinoceros, mammoth, &c. 
Palmntology . The science which treats of fossil remains, both animal 
and vegetable. 
Pelagian. Belonging to a deep sea. 
Petroleum. Mineral pitch; a liquid approaching the consistence of tar, 
of a bituminous odor, and which oozes out of a rock. 
Phlegrmn fields. The burnt fielils; applied by the Greeks to the region 
around [Naples, from the marks of igneous action every where visible. 
Pisolite. A stone composed of rounded particles like peas, agglutinated 
together. 
Pliocene. An era or period analogous to the present, and more recent 
than the miocene. A large proportion of the animal remains of the 
pliocenehtrdita. still exist. 
Porphyry. A rock having a base whose structure is more or less com- 
pact, in which there are disseminated crystals of feldspar. 
Productus. A bivalve fossil shell, concave on one side and convex on 
the other. 
Plastic clay. One of the beds of eocene tertiary period. 
Plesiosaurus. A fossil extinct reptile, having a close resemblance to a 
lizard. 
Precipitate. The fine powder which separates from solutions after stand- 
ing, or which are disengaged by the chemical action of bodies added 
to those solutions. 
Puraice. A light spongy lava. 
Puddingstone. Indurated or cemented masses of rounded pebbles, sand, 
&c. 
Pyrites. A mineral composed of sulphur and iron, or sulphur and copper. 
Quartz. The term universally applied to a simple mineral composed of 
nearly pure silex. Rock crystal is an example. 
Rock. A term applieJ to all mineral beds or masses. 
Sandstone. A rock composed of grains of sand. 
Saurians. Animals belonging to the tribe of lizards. 
Saccharoidal. Resembling loaf sugar. 
Schistj schistose. Slate and slaty. 
Septaria. Flattened balls of stone traversed by seams of calcareous spar, 
or some other mineral. The outer surface has the appearance of a 
turtle's back; and hence they have been considered, by persons of 
little observation, as petrified turtles. 
Shale. Generally used as synonimous with slate. 
Shell marl. The name is applied to recent fresh-water deposits, which 
consist of marl and numerous shells of Helices, Planorbis, &c. inter- 
mixed. 
Shingle. Beaches and shores covered with water- worn pebbles and gravel. 
