300 GENERAL COMPARISON OF 



that at the points of reversal the strata must necessarily 

 become vertical, as was proved to be the case in the 

 central line more particularly. 



The portions of the secondary strata occurring in these 

 islands are so small, since they are only to be found 

 in Seil and Inish Capel, that they scarcely admit of any 

 general comparison. But if the scattered portions ex- 

 isting on the neighbouring continent be included with 

 them, they will be found associated by a common feature 

 which is not uninteresting. This is the general con- 

 formity of their dip, however detached they may be 

 in position. From this it might be judged that they 

 had once possessed a connexion more intimate, and were 

 the remains of a more universal deposit ; while the same 

 circumstance indicates that their present separation is not the 

 result of violent and local causes, but was produced by ope- 

 rations of a gradual nature. I need not however dilate on this 

 subject, as the same circumstance was already pointed out 

 in considering the general connexions of the Trap islands. 



This appearance is further connected with another 

 question of a general nature respecting the positions of 

 strata, which is at present far too obscure to admit of 

 a satisfactory solution. It has been shown that the 

 secondary strata in Mull are deposited indifferently both 

 on the edges and surfaces of the primary, maintaining 

 nevertheless their own regular stratification. In the pre- 

 sent case also, whatever the inclinations of the latter 

 may be, the former maintain a generally regular western 

 dip. Hence it may be concluded that they were de- 

 posited in these places after the primary rocks had 

 assumed their present positions ; and in this case they 

 cannot have undergone any material subsequent derange- 

 ments, but have originally been placed in the inclined 

 manner in which they are now found. Nevertheless there 

 appear to be satisfactory proofs that in other cases the 

 secondary strata have undergone considerable changes 

 of position since their original deposition; an example 



