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are grouped together is various. Marble and ser- 
pentine are usually found uppermost ; but granite, 
though it seems to form the foundation of the 
rocky strata of the globe, is yet sometimes dis- 
covered above micaceous schist. 
The secondary rocks are always incumbent on 
the primary ; the lowest of them is usually grau- 
wacke ; upon this limestone or sandstone is often 
found ; coal generally occurs between sandstone 
or shale \ basalt often exists above sandstone and 
limestone ; rock salt almost always occurs associ- 
ated with red sandstone and gypsum. Coal, basalt, 
sandstone, and limestone, are often arranged in 
different alternate layers, of no considerable thick- 
ness, so as to form a great extent of country. In 
a depth of less than 500 yards, 80 of these differ- 
ent alternate strata have been counted. 
The veins which afford metallic substances, are 
fissures vertical or more or less inclined, filled with 
a material different from the rock in which they 
exist. This material is almost always crystalline ; 
and usually consists of calcareous spar, fluor spar, 
quartz, or heavy spar, either separate or together. 
The metallic substances are generally dispersed 
through, or confusedly mixed with these crystal- 
line bodies. The veins in hard granite seldom 
afford much useful metal ; but in the veins in soft 
granite and in gneis, tin, copper, and lead are 
found. Copper and iron are the only metals 
usually found in the veins in serpentine. Mica- 
ceous schist, sienite, and granular marble, are sel- 
dom metalliferous rocks. Lead, tin, copper, iron, 
and many other metals, are found in the veins in 
