74 WILLIAM H. HOBBS 



Bertrand, later worked out by Schardt, Suess, Lugeon, Termier, 

 Heim, and others. 



It should not be forgotten that there are in the Alps some 

 natural conditions which are favorable to the solution of its struc- 

 tural problems, and without which it seems likely that we should 

 have advanced but slowly toward the goal. The rocks of which 

 the Alps are composed are very largely sediments, which in a 

 considerable portion of the area are uncrystalline and so richly 

 fossihferous that it has generally been possible to determine the 

 place of each local bed within the vertical column. Almost as 

 important in view of the peculiar character of the deformation, 

 there is a horizontal differentiation of the beds from the north- 

 west to the southeast which is recognized both in the petrographic 

 character and in the fossils of the several formations. Thus it 

 has been possible upon this basis to determine in some measure the 

 lateral as well as the vertical displacements of the beds. 



To a small extent only and in relatively few of the significant 

 . localities have the beds been greatly altered through the intrusion 

 of igneous masses; and the regional metamorphism has seldom 

 been so great as completely to destroy the identity of formations. 

 Sculptured by glaciers into a fretted upland, the sheer mountain 

 walls of the Alps, bare as they are of vegetation, often reveal in 

 wonderful perfection all the intricacies of their complex structure. 

 Thus with all its complexity the great problems of Alpine struc- 

 ture appear to be soluble, and it is easy to see that if differences 

 of opinion still exist, we are none the less slowly approaching the 

 goal. 



To all these natural advantages for study there are to be added 

 the network of mountain railways which surpass anything of the 

 kind to be found elsewhere, a wealth of good hostelries, even at 

 high and not easily accessible points, the numerous refuges, and 

 the fraternity of competent and hardy guides. 



For some other regions, such for example as that of south- 

 western New England, no one of the above-mentioned natural 

 conditions is realized, and there is therefore good ground for 

 believing that the problems of structure are in consequence prac- 

 tically insoluble. It is the author's belief, based upon many 



