DIKES AND FAULTS. 
127 
elevated 700 feet, and we might therefore expect 
to see a corresponding elevation of the ground on 
that side of the fault, as represented by the dotted 
line 0, O, and that the strata would thus form a hill 
700 feet high, whereas the ground is level. It is a 
remarkable fact, that in all coal-fields that we have 
any knowledge of, an elevation or depression of the 
strata have no effect whatever in deranging the 
level surface of the earth. 
Every rent or fissure that causes a dislocation of 
the strata may be called a fault ; but fissures filled 
with metallic ores and crystallized mineral matter 
are called veins. The faults that intersect coal- 
fields are sometimes filled with basalt, and are call- 
ed basaltic dikes ; more frequently faults are filled 
with clay, sandstone, sand, and fragments of stone. 
In explaining the cause of this phenomenon, Mr. 
Bakewell remarks, "That the strata of the coal- 
formation have been submerged under the ocean, is 
completely established by the occurrence of marine 
beds over many of our coal-fields. It is farther 
proved, that the faults which occur in coal-fields are 
of different ages; some of them dislocated the coal- 
strata before the marine strata were deposited over 
them, for the faults do not disturb nor displace the 
superincumbent beds : other faults are of a more re- 
cent date, and have cut through both the coal-strata 
and the limestone which covers them. 
" Practical miners, as well as geologists, have 
generally contemplated the removal of the strata 
upraised by faults as having taken place from th6 
present surface of the land ; and have regarded the 
strata as composed of hard beds of sandstone and 
shale ; and have overlooked the original condition 
of these strata before they had been raised above 
the level of the sea, and were indicated by drainage 
and pressure. In their original state, these beds 
were chiefly composed of mud and sand, saturated 
with water, and, therefore, could possess but little 
adhesion. 
