228 PRIMITIVE LIMESTONE. SERPENTINE. 
This is a widely-extended rock ; it sometimes forms 
whole mountains, and even chains of mountains ; but 
these usually have a gentle acclivity. The summit of 
the celebrated mountain called Skiddaw in Cumberland 
is of clay slate. 
258. PRIMITIVE LIMESTONE is a simple mountain 
rock of crystalline or granular structure ; and generally of 
white, yellowish, greenish, or reddish colour. 
To this species of rock belong many of the rich and 
beautiful kinds of marble already described (143, &c.). 
Carrara, or statuary marble (146), is a familiar instance 
of it. Whole mountains in Stiria, Carinthia, Carniola, 
and the Pyrennees, and three mountains in Switzerland, 
10,000 feet in height, are of primitive limestone. The 
mountain of Filabres in Spain, is said to consist of one 
block of white granular marble, 2,000 feet high, and 
three miles in circuit; without intermixture of other 
earths or stones, and almost without a fissure. 
Various mineral ores, in beds and veins, as lead, 
zinc (241), and iron, are occasionally found in this 
kind of rock. 
259. PRIMITIVE TRAP is a mountain rock composed 
of a black mineral called hornblende, mixed, in some varie- 
ties, with felspar (110), and, in others, with mica (123). 
The word trap is of German origin, signifying a 
stair ; and rocks of this formation are called trap rocks, 
because their strata, when exposed, usually jut out, 
one beneath the other, somewhat like a stair. Under 
this term is comprehended a series of rocks, distin- 
guished chiefly by the hornblende, which they all con- 
tain. 
Rocks belonging to this formation are numerous. 
They occur in Scotland ; and abundantly in Derby- 
shire and some other parts of England. In many coun- 
tries they constitute considerable hills. They abound 
in ores. 
260. SERPENTINE is a primitive rock, usually con- 
sisting of quartz (76), magnesia (198), alumine (197), with a 
portion of oxide (21) of iron. 
