144 STUDIES, SCIENTIFIC AND SOCIAL chap. 



shown by the fact that certain ancient terraces of erosion 

 and deposits of river-gravel, seen on both sides of the lake, 

 have been tilted up. From a point midway between the 

 two extremities of the lake they gradually rise higher and 

 higher in the direction of Zurich, until they reach their 

 culminating point at Miinnedorf and Kapfnach, some nine 

 or ten miles above Zurich. Obviously, the terraces in 

 question are the work of the Linth, and must have been 

 formed before the lake came into existence. But surely 

 the simple explanation is that here, as in so many other 

 regions, fluviatile erosion has kept pace with, or even 

 exceeded, crustal deformation. The old river Linth has 

 behaved just as other rivers under similar circumstances 

 — it has cut its way across a gradually-developing deforma- 

 tion. Aeppli, following Heim, believes that the upper 

 part of the lacustrine hollow (i.e., between Mannedorf and 

 the head of the lake) has been caused by a depression of 

 the great Alpine massif, producing a reversal of the valley- 

 slope. But since such a movement will not account for 

 the lower section of the hollow (i.e., between Mannedorf 

 and Zurich), another movement is invoked to explain its 

 occurrence. We are asked to believe that the portion 

 referred to is due to flexing and folding — a continuation 

 of the flexures of the Jura mountains. It seems to me 

 just as easy to believe that the entire lacustrine hollow 

 occupies an area of special depression ! That flexing and 

 folding have taken place cannot be doubted, but there is 

 nothing whatever to show that the river Linth was in- 

 capable of cutting across the inequalities as fast as these 

 were developed. Even if we could accept Heim's notion 

 of a depression of the Alpine massif, and believe with him 

 that the slope of the old valley was in this way reversed, 

 we should not necessarily be able to account for the exist- 

 ence of Lake Zurich. Any great crustal movement of 

 the kind, we have no reason to doubt, would be gradual — 

 so gradual and protracted that the river would continuously 

 fill up the slowly-deepening depression, and thus a lake 

 could not come into existence. [In illustration, I may 

 refer to the deep basin in the valley of the Rhine in Hesse, 

 the bottom of which is 270 feet deeper than the lowest 



