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, 0, 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. 

 Bakevvell 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. 



u Practical miners, as well as geologists, have 

 generally contemplated the removal of the strata 

 upraised by faults as having taken place from the 

 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. 



