4 i2 SCIENCE PROGRESS. 



In the discussion on overfolding, Professor Lapworth 

 practically recognised every stage; from the condition 

 where no separation of arch limb, middle limb, and 

 trough limb had taken place, and where the middle limb 

 has been rolled out between the arch core and trough 

 core (this being Heim's theory for the Doppelfalte), 

 to that wherein dislocation actually ensues ; in which 

 case the arch portion travels in a rigid mass over the 

 trough. It will therefore be seen that Lapworth practi- 

 cally adopted Heim's conclusions, with all their far-reach- 

 ing hypotheses. 



Applying these to the Sutherland area, he concluded 

 that, far from dealing with a simple succession, the Upper 

 Gneiss represented only a part of the Sutherland gneisses 

 that had undergone one of these tremendous overthrusts, 

 the rocks taking part in the movement having suffered 

 great deformation and contortion, thus giving rise to those 

 sheared and pseudo-foliated structures, which he has in- 

 cluded under the term " Mylonitic ". 



Almost simultaneously Dr. Callaway came to a similar 

 conclusion, whilst Dr. Hicks announced that the highest 

 beds were, in fact, parts of the oldest rocks occurring in a 

 broken anticlinal, and Professor Bonney likewise showed 

 that the coarsest gneiss had been crushed into a perfectly 

 schistose rock. 



Powerful as were the facts and arguments brought 

 forward by these various observers in weakening the posi- 

 tion of the Murchisonian hypothesis, its final overthrow was 

 only achieved by the publication of Sir Archibald Geikie's 

 letter, and the first summary on the survey work of the 

 Durness-Eriboll area (9), and thus, by the frank adhesion 

 of the Geological Survey, was closed the excited contro- 

 versy, the views as originally propounded by Professor 

 Nicol, and rejected during so many years, being to a great 

 extent triumphantly vindicated. 



It was now recognised that these Scottish rocks, first 

 commencing as gentle foldings, steepened gradually on the 

 western front until, bending over, they became disrupted, 

 and the eastern limb pushed forward. Reversed faultings 



