Chap. IV.] 



NAHUN AND S^VALIK GROUPS. 



109 



denuded bank of the beds e, which probably were also more or less tilted 

 at the time of formation of the younger deposits. The difference between 

 the two sections, at Tib and in the Markunda, may be explained by 

 supposing that the bank or cliff was less steep at Tib, but chiefly, and 

 more generally, by the admissible assumption that the lateral compress- 

 ing force, to which we may attribute the reverse underlie of the contact in 

 the Markunda, and elsewhere, met with different conditions of resistance 

 in the Tib section. The contact exhibited in this little section 

 precludes the possibility of a fault, and, if there be none here, it were 

 gratuitous and against probability to suppose any in the Markunda section. 

 I believe, therefore, that the overhanging contact in the Markunda section 

 is entirely an effect of a contorting force upon a very steep edge of 

 deposition. 



The interest attaching to this explanation is very great, for the pheno- 



Its modification by men0n t0 wMch ** is a PP lied is one of ver Y ex ^n- 

 lateral compression. g ^ ve occurrence, and the usual modes of accounting 



for it, by inversion or by reverse faulting, involve the conception of causes 



and conditions from which it is a relief to find even a partial escape.* But 



there are, of course, corresponding difficulties introduced : the amount of 



lateral yielding must be inversely as the steepness of the original junction, 



and directly as the depth of the contact which has to jpe accounted for. 



Thus, I can conceive an original contact, like that in Fig. 14, resulting, 



Original junction of succeeding deposits. 



* It is evident that the explanation given of the reversion of this natural junction is 

 applicable also to reverse faults ; a fault that was originally normal might, by a very moderate 

 amount of unequal lateral movement, become reversed. 



