Vol. 62.] RECUUBEXT FOLDS PRODUCED AS A RESULT OF FLOW. 719 



the obstacle O v while still farther on are a few scattered fragments, 

 which may be compared with ' klippen.' In this instance, the 

 several lobes of a complex fold would appear to have been sheared 

 away from each other, passing through a series of stages such as 

 are suggested by the folds in fig. 1. 



If a flow has taken place in the Alpine regions at all comparable 

 with that of these experiments, it is obvious that particular beds 

 may have been very far from continuous at the conclusion of the 

 movement. Thus, if we regard the layer just referred to as repre- 

 senting a limestone-series in the Alps, we might expect, on leaving 

 the region of the ' klippen,' to enter another of recumbent folds ; 

 ascending the mountain-core O v we should find on its 'stoss'-side 

 patches of the series, showing obvious signs of excessive pressure ; 

 and then we should have to traverse the wide interval between 

 the two crystalline masses O x and o before we again encountered 

 insignificant remnants of the original sheet. The absence of the 

 limestone-series between these several points might not, therefore, be 

 the result of denudation, but the natural consequence of mountain- 

 movement. If so, the removal of the stupendous masses of sedi- 

 ment by subaerial agencies, to which the Alps bear such striking 

 witness, is brought closer to our powers of comprehension, since 

 the material thus removed may have been the softer, more mobile 

 argillaceous rock already deprived of its stiffening of comparatively- 

 rigid strata. 



Since, in the first experiment, it is only the first four layers that 

 have assumed a complex folded character, and since these were the 

 only layers which were compelled to make a somewhat abrupt ascent 

 on passing over the obstacle 0, it w^ould appear probable that the 

 folding stands in some relation to this fact. Such a suggestion is 

 confirmed by reference to the illustration given in my previous paper, 1 

 where the layers marked 1 and 2, which commenced their existence 

 wholly behind the barrier, have only taken the first step towards 

 surmounting it, by forming comparatively-simple folds. It is in 

 this region then, immediately behind an obstacle, that the produc- 

 tion of folds originates, and the reason is clear: the anterior extremity 

 of the layer is in contact, either with the floor of the experimental 

 trough, or with the back of the obstacle, and in these regions the 

 flow of the pitch is greatly retarded or even arrested by adhesion or 

 excessive friction. The layer is held fast at this extremity, and as 

 an upward and forward movement of the pitch takes place imme- 

 diately behind, the layer is bulged upwards and forwards in the 

 form of a fold. Slight inequalities of friction between the coloured 

 layers of pitch and those to which pigment has not been added, 

 may bring about the formation of secondary folds. In making these 

 comparisons between flowing pitch and mountain-movements, I am 

 anxious not to push the analogy too far ; but observation has already 

 so greatly outpaced explanation, that even remote resemblances ma}' 

 possess some value. 



1 Quart. Journ. Geol. Soc. vol. li (1895) fig. 3, p. 364. 



