182 LIFE OF SIR JOHN LUBBOCK ch. 



An Experiment in Mountain-Building, 



BY THE 



Right Hon. the Lord Avebury, 

 P.C, D.C.L., LL.D., F.R.S., F.G.S. 



Many years ago Sir James Hall illustrated the forma- 

 tion of folded mountains by placing layers of cloth 

 under a weight, and then compressing two of the sides 

 so that the cloth was thrown into folds. Since then, 

 other and more complete experiments of the same kind 

 have been made by Favre, Cadell, Daubr^e, Willis, 

 and Ruskin. 



In these experiments the compression was from two 

 sides. If, however, folded mountains are caused by 

 compression due to the contraction of the earth, the 

 compression must take place in two directions at right 

 angles one to the other. 



With the view of illustrating this I consulted Mr. 

 Horace Darwin, and he constructed for me an apparatus 

 consisting of four square beams of wood, resting on a 

 floor, which by means of screws could be moved nearer 

 to, or farther from, each other. The beams left between 

 them a space 2 feet across and 9 inches in depth. 



In the square central space I placed some pieces of 

 carpet-baize and layers of sand, each about 1^ inches 

 deep. About an inch above the upper layer of sand I 

 placed a piece of plate-glass and some weights. The 

 machine was then set in motion, causing the beams of 

 wood to approach one another. The sand rose in the 

 centre, until it reached the glass, when it was flattened 

 out. 



On removing the upper layer of sand, the top-piece of 

 cloth shows the upper surface gently undulating in the 

 centre, with some steep folds near the edges, and one 

 slight ridge crossing the plateau at right angles to one 

 of the folds. 



On removing the underlying layers of sand, the next 

 layer of cloth shows two main lines of elevation ; one 

 running from each corner, and consequently crossing 

 at right angles. The whole surface forms a series of 

 winding and curving ridges with intervening valleys, 

 and gradually rises to a culminating dome a little on 

 one side of the centre, where the two main ridges inter- 



