FOLDS AND FAULTING. 407 



logical strata transformation with faulting predominates ; 

 whereas, in the older, transformation without fracture be- 

 comes more and more common, and gives as a further 

 result the fact that the outer chains consist of Mesozoic 

 rocks with beautiful gentle curvatures, whereas the inner- 

 most most ancient ones are much more sharply and ir- 

 regularly bent. 



This, then, is his broad principle : Where rocks have 

 been gradually depressed under a mass of sedimentary 

 strata they will pass more or less readily into that condition 

 suitable for the development of pure folding. Supposing, 

 therefore, 3000 feet of superincumbent strata should suffice 

 to induce the necessary change in clayey materials, it would 

 require a far greater weight to render massive limestones 

 sufficiently plastic to obtain the like result. 



In an eloquent chapter (Theil ii., pp. 1 14-128) Pro- 

 fessor Heim attacks a position which had already been 

 proved untenable, and by showing the eruptive rocks of 

 the Alps to be in every case older than the main upheaval, 

 he has effectually dispelled the reasoning which would 

 attribute to them the cause of mountain formation. If 

 there be any who, on the basis of Lawson's study of the 

 gneiss in the Rainy Lake region, regard most of these as 

 of very late intrusion, they have before them a most diffi- 

 cult task should they attempt to apply their theory to the 

 whole of the Alpine gneisses. 



The conclusion arrived at by Professor Heim respecting 

 the Alps is decided and clear. He refuses to admit that 

 they have been elevated by eruptive agency ; the rocks are 

 older, and have been brought to their present position in a 

 passive manner, and he maintains that erupti\ r e rocks do not 

 produce a mountain chain. He affirms that everything at 

 present known as to the structure of the crystalline rocks 

 composing the Centralmassif agrees absolutely with the 

 conception that they are the arched portion of a fold system 

 of the crystalline earth crust. The crystalline rocks are 

 frequently bent in such a manner at their point of junction 

 with the sedimentaries that they agree more or less closely 

 with them as regards position. The sedimentary rocks, 



