ZURICH AND GLARUS. l8l 
Steep calcareous strata form a wall lOO to 150 
metres high, but very narrow. At one place the 
rock has weathered away, leaving an opening 16 
metres high and 20 metres broad, known as Martin’s 
Loch. It is so high over Elm that twice in the year, 
on the 4th and 5th March and the 14th and 15th 
September, the sun shines through it on to the spire 
of the village church. 
But we may ask why is there this extraordinary 
amount of folding and contortion in the Glarus dis- 
trict between tire Walen See and the Vorder Rhine? 
If the general explanation of the structure of the 
Alps which has been given in previous chapters be 
correct, it follows that the amount of folding in any 
section must be approximately equal. Now im- 
mediately to the east and west the great Glaius 
double fold is represented by a number of smaller 
ones. Further still it is replaced, and the necessary 
economy of space is obtained, by means of the 
Central Massives. In fact, if we look at the map we 
shall see that in the district of the Alps correspond- 
ing to the double fold, from the St. Gotthard on the 
west to the Silvretta on the east, there is no Central 
Massif. The Central Massif and the double fold are 
complimentary to, and replace one another.* In fact, 
* Rothpletz (Geotektonhche Problcme) has propounded an- 
