328 



FAULTS 



the lode has been very considerable. It is usual to speak of a fault as if the fissure 

 had actually moved the lode. It should be understood that an actual movement of 

 great masses of the solid earth is implied, and consequently, the lode having boon 

 formed before the movement, it is moved with the rock in which it is enclosed. Fig. 

 844 is the plan of veins 1,2, 3, 4, and an elvan course a a, which have been dis- 

 located along the line b, c, and all the lodes and the elvan course moved. In this 

 case the movement has probably taken place from the North towards the South. This 

 disturbance will be continued to a great depth, and in fig. 843 is a section showing the 

 dislocation of a lode into three parts. In this case the movement has probably been 



842 



the subsidence of that portion of the ground containing the lode b, and the further 

 subsidence of that portion containing the lode a ; the condition of the surface being 

 subsequently altered by denudation. The inclination of a lode is frequently changed 

 by these movements, thus fig. 845 supposes c d to represent the original condition of 

 the lode ; by a convulsion, the portion a b has fallen away leaving a chasm between, 

 and the ' dip ' or inclination of the lode is therefore materially changed. The direction 

 of the lode is frequently altered by those movements. Many lodes in Cornwall 

 have a direction from the N. of E. to the S. of W. up to a fault, on the other side of 

 which the direction is changed from the S. of E. to the N. of W. Where these dis- 

 turbances are of frequent occurrence, the difficulties of mining are greatly increased. 



The dislocations and obstructions found in coal-fields, which render the search for 

 coal so difficult, and its mining so laborious and uncertain, are the following : 



1. Dykes. 2. Slips. 3. Hitches. 4. Troubles. 



Tho first three infer dislocation of the strata ; the fourth, changes in the bod of coal 

 itself. 



1. A dyke is a wall of extraneous matter, which divides all the beds in a coal-field. 



Dykes extend not only in one lino of bearing through coal-fields for many miles, but 

 run sometimes in different directions, and have often irregular bondings, but no sharp 

 angular turns. When from a few feet to a few fathoms in thickness, they occur some- 

 times in numbers within a small area of a coal-basin, running in various directions, 

 and even crossing each other. Fig. 846, represents a ground plan of a coal-iicld. 



