GENERAL STRATIGRAPHY, 45 



that the area now under notice affords an excellent example of such 

 conditions : we have seen that all the leading circumstances suggest this 

 hypothesis^ and I have adduced the folded or faulted flexure north of 

 Ryak to corroborate this view; it seems, indeed, self-evident that the 

 force which produced this feature was directed from the south, the axis- 

 plane being also inclined to that point. It has been observed, however, 

 that this is by no means generally the form of the flexures in these 

 strata ; the case is decidedly the reverse ; the normal flexures, whether 

 uniclinal, or anticlinal with one slope very flat, have their axis-planes 

 underlying northwards. So much is this the rule that, if from other 

 considerations it can be independently established that the contortions in 

 this region are the result of a depression to the south and the consequent 

 compression of the strata, it would be inferable that one result of such 

 a process, at some stage or other, is the production of normal flexures 

 having their steeper sides towards the basin of depression, or, having 

 their axis-planes underlying from the centre of subsidence. It would be 

 valuable to know what light the abstract consideration of the case 

 could throw upon the law thus indicated. 



Once the form of the flexures is struck out by any initial stage of 

 movement, all subsequent action must be guided thereby. In this way, 

 it has occurred to me that the feature north of Ryak may not be a 

 bond fide normal flexure of the kind described, one that from the begin- 

 ning had its present southerly underlie. It may well be that a farther, 

 or a slightly different, lateral pressure might produce such a feature out 

 of one of the ordinary normal flexures of the district with a northerly 

 iinderUe, such as that seen at the south end of the section. The compo- 

 sition of this ridge at Ryak encourages such an interpretation : the thick 

 band of shales accompanying the coal that occurs in about the middle of the 

 cretaceous group here, appears just along the north flank of the ridge ; 

 and it is tremendously- crushed. The slipping or faulting, which the 

 supposition I make requu-es, would seem to have taken place along these 

 A 1 ( 195 ) 



