ROCKS OF THE NORTHERN HIGHLANDS. 377 



admitted Hebridean. If the foliation does not represent bedding, 

 it represents current-lamination, cleavage, or something else. 



Passing over current-lamination as obviously out of the question, 

 let us examine the cleavage hypothesis. A few considerations will 

 show its inapplicability. 



(1) Cleavage-planes are uniform over large areas ; but the planes 

 in the " Logan " often dip, within a square rood, in more than one 

 direction, their strikes sometimes bend sharply round, and they are 

 contorted precisely as in the case of ordinary strata. 



(2) Cleavage-planes cut across bands of varying composition; 

 but the planes of fission in the " Logan Rock " coincide with such 

 bands. 



(3) Cleavage-planes are not confined to certain horizons, leaving 

 rocks above and below which are susceptible of cleavage unaffected. 

 But shales and grits which rest upon the " Logan Rock " in Ben 

 More, and similar strata below the " Logan " of Glen Coul, present 

 but slight traces of cleavage ; and such cleavage as exists does not 

 coincide in strike with the foliation of the gneiss. 



If it be suggested that this foliation is the result of some un- 

 known force, I can only reply that it will be time for me to examine 

 this cause when it has been discovered. Meanwhile I am justified 

 in working on the accepted principles of our science. 



3. The strata below the " Logan Hock " not metamorphosed. — The 

 " Logan Rock'' is as highly metamorphic as the Hebridean, but the 

 underlying rocks have undergone little change (see p. 359). Now 

 I do not affirm the impossibility of contemporaneous metamorphic 

 rocks resting on unaltered beds ; but I do not know of such a 

 relation in the British Isles. Such cases have, indeed, been alleged 

 to occur in North Wales and Ireland ; but after studying most of 

 these instances in Wales and some of the most critical in Ireland, 

 I am compelled to reject them, the apparent superposition of the 

 metamorphic rocks having been ascertained, in every section exa- 

 mined, to be due to dislocation. When, therefore, we find highly 

 crystalline gneiss overlying shales and slates, our experience in the 

 British area raises a strong presumption against the contemporaneity 

 of the metamorphic rocks. I have already shown (p. 359) that the 

 phenomena cannot be explained by selective metamorphism. 



4. No beds of passage between the " Logan Rock " and the rocks 

 above and below. — If any formation intercalated between others had 

 been metamorphosed, we should expect some signs of transition 

 between the metamorphic and the unaltered rocks. Such evidence 

 is, indeed, offered by Dr. Heddle. Thus he states that, on Cama- 

 loch, the " Logan Rock " occurs in the " Upper " Quartzite " in five 

 closely adjacent beds." Having studied the locality, I am unable 

 to accept this reading. There is abundant evidence of excessive 

 contortion, crushing, and dislocation ; and the alleged intercalations 

 I believe to be merely repetitions by faulting. Similar facts are 

 stated to occur in Glen Coul, in a section which I visited under the 

 obliging guidance of Dr. Heddle. I was not satisfied with the 

 evidence then adduced; and the facts collected at the time, confirmed 



