138 OUTLINES OF FIELD-GEOLOGY 



to point ; if we felt any uncertainty as to its course 

 through some part of the country, we should make the 

 line there a broken or dotted one. 



The side of up -throw or down -throw may either 

 be fixed at once from our knowledge of the order of 

 succession among the rocks, or may be determined at a 

 later stage, as our acquaintance with the district increases. 

 Thus, in the case which has just been under notice, if 

 we knew that the granite series was older, that is, under- 

 lay the other, we should say that the up-throw of the 

 fault was to the granite side. This direction might be 

 marked on the map by a short bar placed perpendicular to 

 the line of the fault, and on the down-throw side. In the 

 completed map the fault might be shown by a strong black 

 line or by a white line. The latter method is adopted on 

 the maps of the Geological Survey of Great Britain, where 

 fine lines of opaque Chinese -white are placed over the 

 geological colours to mark the position of the faults. 



From the example given in the diagram which we 

 have been considering in detail (Figs. 27, 28), it appears 

 that one indication of the proximity of a fault may be a 

 rapid rise in the angle of inclination of strata. It is 

 common to find the beds on the down-throw side bent 

 up against the other side, and this upturning may extend 

 for a few feet or for more than a mile. The amount of 

 disturbance may be regarded as bearing on the whole a 

 relation to the amount of vertical displacement of the 

 fault; though to this conclusion there are many ex- 

 ceptions. The great fault already referred to as flanking 

 the Scottish Highlands has placed the Old Red Sand- 

 stones and conglomerates on end for about two miles. 



