148 SCIENCE PROGRESS. 



Alps are rendered accessible by roads and railways. The 

 Eastern Alps are the playgrounds of the two foremost 

 Continental schools of geology, Vienna and Munich. The 

 great bow of the Western Alps has no such advantages. 

 The most critical part of the area is a frontier line, which 

 has little hotel accommodation, and attracts few visitors. 

 The military authorities, moreover, do their best to make 

 this number even smaller still. The only geological maps 

 are on a small scale and very diagrammatic. Nor is there 

 any prospect of anything better for much of the area being 

 attempted for some time to come. So the present plethora 

 of hypothesis may long continue. During the past two 

 years numerous important additions to the literature of the 

 area have been made, but these show how far we still are 

 from any agreement upon even the fundamental facts. 



In the first place it is necessary briefly to summarise 

 the main outlines of the structure of the Western Alps. 

 As is shown in fig. i these consist of a series of concentric 

 chains l which sweep round from Lucerne and the St. 

 Gothard through the districts of Geneva, Mont Blanc, 

 Dauphine, and the Cottians to the Apennines. The most 

 persistent zone is that of the "Zone du Brian^onnais," 

 which consists in the main of a band of Carboniferous, 

 Triassic and Lower Jurassic rocks which extends from the 

 St. Gothard to Genoa. To the east and west of this are 

 two zones formed of schistose rocks, and containing many 

 great "massifs" of gneiss. These gneisses were originally 

 described as the oldest rocks in the zones, but they are now 

 known, in many cases at least, to be of later date than the 

 schist and of an eruptive character. The zone to the east 

 is known as that of Monte Rosa ; the one to the west as 

 that of Mont Blanc. Outside the latter is a band of lime- 

 stone composed in the main of Jurassic and Cretaceous 

 rocks. On the north side of the curve there is a zone not 

 represented to the west ; this comprises the zone of the 

 Prealpes, including the groups of Chablais, south of Lake 



1 The distribution and composition of these chains have been clearly- 

 summarised by Dr. Diener in his Gebirgsbau der Westalpen, 1891. 



