658 PRINCIPLES OF STRATIGRAPHY 



The village of Horgen is situated on the -southern shore of the 

 Lake of Zurich. The shore, which is here composed of the sand- 

 stones and marls of the Mollasse, was covered originally by sand, 

 gravel and clay in the upper part, and this, near the shore, was un- 

 derlain by soft muds, which extended lakeward, covering the rocks 

 to the center of the lake. On the ground thus underlain with soft 

 mud rests a part of the railroad, which skirts the southwestern shore 

 of the lake (Ziirichseebahn), the Horgen station being built close 

 to the shore. A sea wall was built and the surface raised a slight 

 amount (0.4 to 0.6 meter) by filling-in, but prior to this a number 

 of buildings and a stone-cutting yard were removed, so that on 

 the whole the excess of loading was slight. On February 9, 1875, 

 when the filling in was nearly complete, the new sea wall and the 

 filled area suddenly sank for a length of 135 meters, the lake along 

 the line of the railroad reaching a depth of 7 meters. The examina- 

 tion showed that a part of the bottom layer of soft mud had slid 

 lakeward, so that the more resistant overlying sand and gravel beds 

 came to rest upon the rock surface. The gliding continued until 

 the mud layers had completely bared the rock slopes for a distance 

 of nearly 300 meters lakeward. The most pronounced of these 

 glidings occurred on June 12, 1875, this, however, affecting mainly 

 the sublacustrine mud layers. By filling in a part of the sunken area 

 and carrying the railroad line farther inland, the construction was 

 completed and the line opened for traffic September 20, 1875. The 

 following day was one of heavy rains, and on the morning of the 

 22nd fissures began to open in the made land, the new wall began 

 to crack, and suddenly a part of the wall, 85 meters long, and the 

 station lands and tracks to a width of 23 meters sank beneath the 

 inrushing lake waters. Just before noon a second subsidence took 

 place, a third one followed early in the afternoon, and others fol- 

 lowed on the 23rd and 24th of September. The total area which 

 thus disappeared beneath the water of the lake had a length of 204 

 meters and a width of 48 meters, wdth an area of 6,560 square me- 

 ters. Subsequent glidings occurred in October and November. 



The gliding began on the steeper slopes at a distance from 

 shore, and was then transferred shoreward. The first effect of the 

 gliding of February 9 was the lowering of the outer slope from 

 31 per cent, to 2^ per cent., but the gliding of June 12 caused the 

 complete baring of the rock for a distance of 150 meters or more, 

 and a change of grade back to 30 per cent, or 31 per cent., and 

 even a higher one farther lakeward. This became even more pro- 

 nounced in the glidings of September and later. The total extent 

 of the glidings was 450 meters, and the material was carried out to 



