492 



THE PROBLEM OF THE LIZAED ROCKS. 



By the kind permission of my friend, Dr. Albert Heim, of 

 Zurich, and of his collaborateur, Professor E. de Margerie, of 

 Paris, I am enabled to re-produce some illustrations from their 

 standard work, " Les dislocations de 1' ecoree terrestre," Zurich, 

 1888. And the following is a condensed statement of the theories 

 propounded by these two eminent geologists : — 



The earth movements as evidenced by anticlinal and 

 synclinal foldings, by upheavals and downthrows, fractures and 

 shearings, occurring repeatedly and in varying directions, give 

 rise to such an intermingling and complexity of the rock masses 

 in mountain districts as to make it almost impossible for the 

 most experienced geologist to unravel them, unless he could 

 study the same strata in other localties in a less disturbed state, 

 opportunities for which, fortunately, occur in some parts of the 

 Swiss and Italian Alps ; and thus supplied with an index to the 

 component parts in their original order of superposition, the 

 practical geologist can refer the compressed and transposed 

 fragments to their original strata. 



For this purpose the closest attention to the progressive 

 changes in the shifting position and intermingling of the strata 

 is required, and the following diagrams, begining with the 

 simplest movements, will illustrate the subject more concisely 

 than any lengthened verbal description. 



Thus we have in Fig. 1 the initial anticlinal axis at a right 

 angle to the planes of stratification. In Fig. 2 the axis inclines 

 at two varying angles, and in Fig, 3 the axis is laid so low as to 

 invert the stratification, making the older layer appear to overlie 

 the younger layer. 



