486 ' ON THE PHYSICAL STRUCTURE 



flexure are exhibited on a scale of much extent, these planes are 

 inclined to the perpendicular in a greater or less degi'ee, according 

 to the energy of the inflecting force. In the region before us, the 

 dip of the imaginary plane is almost invariably to the southeast, 

 the amount of the deviation from the vertical altitude diminishing 

 progi'essively, as we cross the chain towards the northwest. A 

 corresponding law of the axis-planes will, we believe, be found to 

 obtain, in all extensive groups of axes, the general expression of 

 their relation being, that the dip of the axis-planes is always to- 

 wards the region of maximum disturbance. From the position 

 thus possessed, by the axis-plane, it will readily appear, that its in- 

 tersection with a horizontal line connecting the southeast and 

 northwest branches of an anticlinal flexure, will lie nearer to the 

 northwestern branch, and that the reverse will be the case in a 

 synclinal bend. For these relations, see Diagrams, Plate XVI. 



Character of the Flexures in each of the Nixe Divisions 

 OF the Appalachian Chain. 



While the flexures of the strata of the Appalachian chain every 

 where conform to the general type above described, they display, 

 in each of its great subdivisions, some one or more prevailing 

 characters, marking, as we think, the degi*ee of energy, and the 

 directions of the disturbing forces. Of these, as exhibited in the 

 several divisions formerly specified, the following is a brief ac- 

 count. 



1. Hudson River Division. In this belt, the flexures are, for 

 the most part, of the closely folded type, and the dip is almost in- 

 variably towards the southeast, the compressed and oblique plica- 

 tion of the beds extending equally to the hypogene, or primary 

 rocks, of the mountains bounding the valley on the east, and to 

 the lower formations of the Appalachian system, which occupy 

 the valley itself. Northwestward of the valley, this folded condi- 

 tion of the rocks gives place, as in the vicinity of the Catskill 

 mountain, to flexures of the normal form, which, as we advance, 

 become comparatively obtuse. 



2. Delaware Division. In this curving district, the formations 



