SUMMER ISLES. GEOLOGY. 85 



The same disposition may be observed in many other of 

 these islands. No apparent cause for this sudden and violent 

 disturbance can be discovered, neither granite nor trap 

 being present ; while it is at variance with the prevailing 

 character of this sandstone, which, on the adjacent conti- 

 nent, is disposed with the utmost regularity, varying but 

 a few degrees from the horizontal position, and thus cover- 

 ing a great space. In Muligrach island the progress of 

 this change is visible ; since the horizontal strata can be 

 traced gradually undulating until they become erected 

 into a position nearly vertical, when the marks of strati- 

 fication disappear.* The change of position is here 

 accompanied by empty fissures and caverns, indicating that 

 some subsidence, or other analogous changes, of a date 

 probably more recent than the last deposits of rock, have 

 been concerned in its production. With respect to the dip 

 of these strata, it is necessarily variable, as the preceding 

 statements will show; yet, throughout the whole group, 

 there is an average general inclination toward the south- 

 east. 



examples of sandstone and gneiss. That there is no conviction in these 

 subjects without actual contact, is a rule of which the geologist should 

 never lose sight. 



* Plate XXXII. fig. 9. 



