November 24, 1892] 



NATURE 



Si 



EXPERIMENTS ON FOLDING AND ON THE 



GENESIS OF MOUNTAIN RANGES.^ 



Method 0/ Investigation; Folding at Different Levels. 



DEFORMATION is represented in an exact manner, 

 if we note the movements executed by certain 



Fig. 3 



Fig. 5. 



Fr;. 7. l'"^- 



points, and the position of these points before and after 

 deformation. I divide the surface of sediments into 

 squares (scale = cim.), and this division passes in 



' Extracted (mm Geologische und Geographische Experimente, by Dr. 

 E. Reyer. i Heft: Defoniiaiion und Gebirtjsbildung. Leipzig, 1892. See 

 also " (.)n the Causes of the Deformation of the Earth's Crust," by the same 

 Author. (Natukb, vol. xlvi. p. 224.) 



vertical direction through the whole system, so that every 

 stratum is divided into prisms or cubes of known 

 dimensions and positions. At every moment of deform- 

 ation we may note the movements of any point or line, and 

 the deformation of any square or prism. Especially the 

 deformations of the surface and of normal-profiles is im- 

 portant. The position (orientation) 

 of prisms must agree with the direc- 

 tion of pressure. 



I employed in every case muddy 

 material (clay, plaster of Paris). Ex- 

 ample : We note the position of 

 prism I. in Fig. I, and its position 

 and deformation are noted in Fig. 2 ; 

 I. is pushed forward and deformed 

 into \.x. B = the " Basal plane," is 

 parallel to the base or surface. No = 

 Normal plane, is situated vertical and 

 in the direction of pressure. L = 

 Longitudinal plane, vertical and at 

 right angles with No, agrees with 

 extension of strata. 



N = normals, i.e.^ perpendicular 

 scale-lines. 



Explaining experiments : The sedi- 

 ments I., II., Fig. 3 (exp. 203, clay 

 with a layer of plaster) are subjected 

 to lateral thrust. The higher parts 

 are more moveable and get deformed 

 more than the lower strata. 



I. goes to \.x, it is compressed and 

 elevated ; II. in contact with the wall 

 is elevated a little (to x). The dark 

 middle stratum I. produces a flat 

 fold. In Fig. 4 compression and ele- 

 vation is more intensive. The nor- 

 mals N (originally vertical lines) are 

 deformed into curves. 



When at the surface very plastic 

 material dominates (mud), the surface 

 after deformation remains flat, whereas 

 in the deeper parts intense folding 

 may have taken place. If we push a 

 muddy mass, covered by plastic layers, 

 the latter get folded, whereas the 

 deep parts are only thickened. 



The movements and deformations 

 of N (normal profile) are of especial 

 importance. 



Fig. 5 (exp. 292), paper between 

 muddy strata. The direction and 

 deformation of normals show the 

 typical movement of strata in each 

 case. 



In Fig. 6 a plastic layer (white) 

 lies between muddy sediments. After 

 the deformation only the white layer 

 is folded. 



In Fig. 7 folding towards the deeper 

 parts is more intense, but the muddy 

 surface remains flat. In all these 

 cases strata get thickened. The 

 thickness measured in a fold-chain 

 does not correspond to the original 

 thickness. The strata of the Appala- 

 chian Mts., having to day a thickness 

 of 10 km. in a certain section, originally had different 

 dimensions. If measured along the fold-limbs the number 

 is by far too small, as here the strata are rolled out ; in 

 the synclines, on the contrary, strata appear much thicker 

 than they were at the beginning. 



If plastic sediments are driven by their own weight,/.* 

 if they i^lide over an inclined plane against an obstacle. 



NO. 1204, VOL. 47] 



