FOLDS AND FAULTING. 411 



Hicks and Callaway, but principally by the work of Pro- 

 fessor Lapworth, who, in a series of papers on the Girvan 

 succession, and the " Secrets of the Highlands," showed the 

 marked influence Heim's work had had upon his own views, 

 the publication of these articles having also the effect of 

 inaugurating the application of the new principles to the 

 problems and difficulties connected with the tectonic 

 structure of our own island. What, then, were the 

 results of these contributions from a tectonic point of 

 view ? 



Undoubtedly, the principal results were : The recogni- 

 tion of the importance of isoclinal folding in the Ayrshire 

 Palaeozoic rocks ; the discovery that zones, when carefully 

 traced out, showed the actual presence of enormous folds ; 

 and that the repetition of the same fauna in upwardly 

 ascending series was the result of the close parallel packing 

 of a group of anticlinal and synclinal folds. The outcome 

 of these labours has also served to overthrow the compli- 

 cated conception of " Colonies " introduced by Barrande to 

 account for the peculiarities observed in the palseontological 

 succession. 



Having thus far successfully endeavoured to elucidate 

 these varied and difficult problems, Professor Lapworth 

 next turned his attention to mountain structure, and was 

 led to the conclusion that folding was the result of lateral 

 compression. He observes : " At the foot of a mountain 

 range the inward thrust and the outward counter-thrust are 

 approximately equal in amount and opposite in direction, 

 and the resulting folds are normal and regular (normal or 

 amphiplexal folds), but as we proceed towards the centre of 

 the range, whilst the thrust inwards remains approximately 

 the same, the counter-thrust outwards is aided by the effect 

 of the gravity of the mass above, and these two unequal 

 forces are applied to the stratum obliquely with respect 

 to each other. As a natural consequence, the axes of the 

 rock folds no longer remain vertical, but slope obliquely out- 

 wards, i.e., in that special direction in which the folding 

 and ascending strata encountered the least resistance to 

 their extension " (Geo/. Mag., p. 198). 



