OF THE MORE DISTURBED ZONES OF THE EARTH'S CRUST. 443 



usually, though not always, by some sudden difference of dip, that we are en- 

 abled to detect the presence and the magnitude of the dislocation. 



It seems also necessary, on this occasion, to explain the effects of those great 

 longitudinal obliquely-dipping faults, when they occur directly in the anticlinal and 

 synclinal axis planes, which are their occasional positions. The same forward 

 upward-sliding, just described as having occurred where the fracture is between 

 the anticlinal and synclinal curves, must have taken place where it has coincided 

 with these, and as the movement must necessarily have been in the same direc- 

 tion, lifting, that is to say, the lower strata cut by the fault, upon the edges of 

 higher and higher beds, in the forward propulsion of the Fi s- 2 - 



flat side of the broken wave, we have no difficulty in un- V" 

 derstanding how fractures in these positions, as well as /\ : : :::; ^illi^ 

 in the other already spoken of, must have given rise to / / /V- -]^ a 

 that very common phenomenon of the dipping of newer ||iS||fflj^^^^ & 

 formations under older ones in plicated and dislocated UVi'-iI'SSK 

 countries, like the Alps and Appalachians. This puzzling ^™^jj| \1K/% J 

 feature of stratification, long an enigma to geologists, can, ^% l%v 



I conceive, be explained upon no other analysis than that ''^Wk 



which is here given, namely, the oblique folding of undu- C ^^V 



lated strata, — the obliquity of the planes of the faults, _ J , , 4 .. r? 



7 x •* * Section of a longitudinal dis- 



either coincident with, or parallel to, obliquely dipping axis section showing the plane of frac- 

 ture and the uninverted strata 



planes, — and the forward upward thrust of the uninverted driven forward upon the inverted. 

 upon the inverted broken strata, through a tremendous tangential force incident to 

 a wave motion. 



Exemplification of the Laws of Flexure, by the Phenomena of some of the 



Undulated Zones of Europe. 



Belgium and the Rhenish Provinces. — Embracing in one view the undulated 

 districts of Southern Belgium, the Rhenish Provinces, the Westphalian coal-field, 

 the Ardennes, the Hundsruck, Taurus, and Hartz ranges, as described and mapped 

 by M. Dumont and other geologists, we can discern most distinctly all the phe- 

 nomena of flexure and of dislocation of the strata, here indicated as charac- 

 teristic of the structure of the Appalachians. We there perceive a wide zone of 

 crust undulations having its strata most invaded by igneous rocks, and most 

 ruptured and metamorphosed, along its south-eastern side, and displaying its 

 most ancient sedimentary formations in a state of close plication, with innu- 

 merable inversions of the dip, imparting to wide tracts one uniform parallel incli- 

 nation towards the south-east. Crossing the zone north-westward, we enter 

 newer and newer strata, until we come to the undulated coal-field of Westphalia 

 or Belgium, our traverse taking us from the non-fossiliferous formations, at the 

 very base of the Palaeozoic system. In whatever meridian we make our section, 



VOL. XXI. PART III. 6 D 



