COAL-FIELD OF CLACKMANNANSHIRE. 133 



no less than 1230 feet, as before mentioned. This 

 last is the greatest dislocation I have met with, or 

 know of, in Great Britain. These slips are fissures, 

 which extend from the surface of the strata or Rock- 

 head, to an unknown depth; and vary in width 

 from a small fraction of an inch, to 4 or 5 yards. 

 The fissure is filled up with heterogeneous matter, 

 composed of all the rocks composing the strata. In 

 the fissure of the great north slip, several thin 

 strata are to be seen lying nearly in a vertical di- 

 rection. Besides these great slips, there are many 

 other small slips parallel to these, and many lying 

 in an oblique direction with the dip and rise line of 

 the coal. Several of these oblique slips produce also 

 great dislocations. 



With regard to slips in coal-fields, we find that 

 there is a general law connected with them as to 

 the position of the dislocated strata, which is this : 

 When a slip is met with in the course of working 

 the mines, — if, when looking at it, the vertical line 

 of the slip or fissure forms an acute angle with the 

 line of the pavement upon which the observer 

 stands, we are certain that the strata are dislocated, 

 or thrown downwards upon the other side of the 

 fissure. On the contrary, if the angle formed by 

 the two lines above mentioned is obtuse, we are cer- 

 tain that the strata are dislocated or thrown up- 

 wards upon the other side of the fissure. When the 

 angle is 90°, or a right angle, it is altogether uncer^ 

 tain whether the dislocation throws up or down on 



