4 02 SCIENCE PROGRESS. 



hypothesis) (2) pointed out that the conditions observed 

 were perfectly compatible with the assumption that lateral 

 pressure, viz., that of masses of the earth's crust against other 

 masses along lines of fracture on the surface, had been the 

 cause of these phenomena. About the same time, Sir R. 

 Murchison (3) had clearly seen that, in those parts of the 

 Alps where crystalline overlay unaltered sedimentary strata, 

 this result would be due to " one enormous overthrow, so 

 that over the wide horizontal area, the uppermost strata, 

 which might have been lying- in troughs or depressions 

 due to some grand early plication, were covered by the 

 lateral extension over them of older and more crystalline 

 masses ". 



In 1856 Professor Nicol (4) hinted at the possibility of 

 such conditions having likewise existed in the Scottish High- 

 lands. " The termination of the Quartzite period seems 

 again to have been marked by convulsions. To these we 

 must refer the action by which the higher portions were 

 converted into gneiss, or this gneiss if a pre-existing rock 

 forced over the quartzite." 



Two years later, Sir R. Murchison (5), examining the 

 same country, was led to a conclusion which for twenty- 

 five years proved a stumbling-block to the larger number 

 of English geologists. To him the succession in North 

 Scotland appeared as a perfectly simple upwardly ascending 

 series, the upper quartzite and upper gneiss being not only 

 apparently, but in reality, younger than the Durness lime- 

 stone they seemed to overlie. To this view the most 

 distinguished amongst our English geologists rallied, and 

 Professor Nicol's protest in 1861 (6) carried no conviction 

 to the minds of the majority. Undoubtedly he weakened 

 his position by doubting the existence of gneissose rocks 

 above the limestone series, and assuming that simple fault- 

 ing might account for all the phenomena observed. Never- 

 theless, in justice it must be allowed that he recognised that 

 "a comparatively very small amount of inversion and ex- 

 trusion of older crystalline masses will suffice to explain any 

 of the vScottish sections, even as drawn and described by 

 the advocates of an overlying younger gneiss ". After 



