Notices from the Minute Books of the Geological Society. 57 1 



8 and 9. These models exhibit the effects of denudation on strata differently 

 inclined, and the inferences which may be deduced respecting the dip of the beds, 

 by attending to the position of the re-entering angle of the strata in transverse 

 valleys of denudation. In No. 8. this angle is pointed up the valley, the strata 

 having been " overcut " or acted upon, nearly in the direction of their dip : 

 in No. 9. the re-entering or V angle points down the valley, in consequence of 

 the greater inclination of the strata and the denuding force having acted obliquely 

 to the dip, and " undercut " the beds or denuded first the lowest, constituting 

 the crest of the hill. In the case exhibited in model No. 8, the observer in as- 

 cending the valley passes regularly from the lowest to the highest strata ; but in 

 the instance represented by No. 9, the highest strata form the lowest part of the 

 valley, and in ascending its course a succession of underlying beds are passed over. 

 Without due attention, however, to the direction of the V angle, the reverse might 

 be inferred, and the strata might be considered to dip into the rising ground, and 

 not obliquely from it. Many points of great interest connected with mining, and 

 dependent upon the direction of the V angle, are pointed out by Mr. Sopwith. 



10. This model exhibits the effects of denudation on the outcrop of strata, the 

 direction of the dip being into the hill or rising ground, and not, as in the two last 

 cases, more or less parallel w4th it. In this instance the V angle appears to point 

 up the valley, but by tracing the outcrop it is found to incline into it, the beds 

 forming the V occupying a higher level on the flanks than in the bottom of the 

 denudation. 



11. The object of this model is to exhibit the effects produced by the intersec- 

 tion of veins on a vertical surface, on an inclined plane, and on a horizontal one 

 (the bottom of the model). The white vein is also shown to be of greater anti- 

 quity than the red, having been dislocated by it. 



12. The last model explains the effects of denudation on a mineral district iden- 

 tical in structure and the amount of disturbance with No. 1 1 . 



