334 RELATION OF FAULTS TO UPHEAVAL. 



Great Dislocations. As far as we know, the greater portion of 

 the convulsive movements of the earth's crust were accomplished by 

 means of " faults." One of the most magnificent examples of dis- 

 location in Europe is that grand break nearly along the line of the 

 western border of Durham and Yorkshire, from near Brampton by 

 Brough and Kirkby Stephen to near Kirk by Lonsdale, the effect of 

 which is to throw down to the west the strata of the Carboni- 

 ferous system more than 1000 yards through a length of seventy 

 miles. An axis of slate rocks rises along the line of fracture, 

 which is also partially marked by dykes of dolerite. On the 

 west the beds dip at high angles to the west ; on the east they 

 decline gently to the east. No proper plane of fault is traceable in 

 this case of enormous disruption, owing to the circumstances of the 

 country. This line of disturbance is cut off to the north by the 

 ninety-fathom dyke, and to the south by the Craven fault ; and 

 there is every probability that it is actually continued along the 

 lines of these faults to a direction right-angled, or nearly so, to its 

 own course. 



Relation of Faults to Axes of Elevation. Amongst these faults 

 it is possible, perhaps, to distinguish two periods of disturbance, the 

 older one marked by a direction nearly east and west, which is that 

 of most of the metalliferous veins, the other by a direction from 

 north to south, which is that of several whin dykes and some few 

 lead veins. These different directions may have taken their rise from 

 the two directions of the axes of convulsion which bound the district, 

 and may mark successive periods of folding, and elevation of the 

 ancient sea-bed still evident in axes of compression. 



The limits of time by which the faults are defined are in many 

 instances nearly coincident with the limits of uppermost Coal-measures 

 and New Bed Sandstone. 



Some cases of disturbance are of a complicated nature. Such 

 are the extraordinary retroflexures of the calcareous strata adjoining 

 the Alps, the retroverted dips in the coal-fields of Somersetshire and 

 Belgium, and the flanks of the Malvern hills. In some of these cases, 

 as on the western side of the Malverns, and the western side of the 

 Appalachian chain, we find the curvature often repeated in many 

 synclinals and anticlinals; we see the slopes on each anticlinal steeper 

 on the western side ; and we remark that the anticlinals, taken suc- 

 cessively from east to west, grow less and less steep, and more and 

 more broad, as we proceed farther and farther from the mountain 

 chain. 



Dykes. 



Dykes are concomitants of volcanic action, which owe their exist- 

 ence to the formation of fissures which extend from below upward, or 

 in the planes of stratification. The fissure forms a vacuum, which 

 draws the igneous rock up into its present position ; and sometimes 

 the fissure, by reducing the pressure, renders the igneous rock fluid. 

 How far dykes may be produced out of the material of the strata 



