294 Scientific Proceedings, Royal Dublin Society. 



Such inversions in the Alps, the Appalachians, and the Hima- 

 layan ranges are on record, one or both of the features of overfolding 

 and thrusting having been put in evidence to explain similar anom- 

 alous relations between altered and other rocks in various mountain 

 regions. On the flanks of the Himalayas the axes of compressed 

 anticlinal folds have been traced by Medlicott, longitudinally 

 resolving themselves into faults, and bordering the western part of 

 that chain there are certain crushed lines of junction between dif- 

 ferent groups, coincident with their strike, which, though I could 

 not exactly call them faults, seemed to have as close connection 

 with the force of thrust, associated with the neighbouring moun- 

 tains, as Mr. Medlicott found reason to believe existed in rather 

 similar positions to the eastward. 



The localization of the evidences of these crust movements, of 

 folding, shearing, thrusting, and metamorphism, points to their 

 intimate connexion with the causes of true mountain structure. 

 We do not hear of them in regions where the rocks are in a state 

 of horizontal repose, even though they may be mountainous regions 

 but belonging to the other kind of mountains left by erosion ; for 

 the reason that disturbance has been absent. In these cases the 

 nearest approach to any lateral movement that I am aware of 

 exists in the sidelong creep described by Mr. Barlow as affecting 

 the walls of the great canons of "Western America, and attributed 

 by him to the vertical presence of superincumbent masses, impart- 

 ing to the underlying beds an internal motion towards points where 

 deep erosion has deprived their materials of support. This move- 

 ment is also shown not to have been accompanied by metamor- 

 phism of the rocks. 



It seems we may fairly gather from the accounts given, that in 

 the Highland province of special disturbance the thrust movements 

 date from the earliest periods, while the more prominent fault dis- 

 locations chiefly belong to much later geological times. 2 How far 

 this may be merely accidental or otherwise does not as yet appear, 

 but there is reason to believe that the earth movements were inti- 

 mately connected with the production of one of the oldest of moun- 

 tain chains — that which stretched from Scandinavia to the north of 



1 Barlow, Quarterly Jour. Geol. Soc, Lon., vol. xliv., p. 783. 



2 Judd, Address to Brit. Assoc, Aberdeen. 



