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next great zone to the southeast, especially near the Delaware, 

 have been disturbed by an anticlinal axis giving them both a 

 northwestern and southeastern dip, the planes of cleavage are 

 observed to maintain invariably a southeastern, or, more properly, 

 a southern inclination, which is usually between 40° and G0° to 

 the horizon. Their strike, or the line formed by their intersection 

 with a horizontal plane, is, therefore, far from coinciding with 

 the prevailing strike of the strata themselves. And it is not a 

 little curious, that this law, of a nearly south-southeast direction 

 in the dip of the cleavage surfaces, holds true, not only of the 

 slate but of all the contiguous formations of the series, except the 

 coarse sandstone and conglomerate rocks of the mountain, affecting 

 the softer variegated shales, beds of limestone, and olive-coloured 

 slates of the still higher rocks, which occupy a breadth of many 

 miles to the northwest. But its vast extent is more particularly 

 seen, when we trace the formations in their longitudinal course 

 along the Kittatinny Valley, where we may behold the cleavage 

 planes preserving their southeastern dip, with scarcely an inter- 

 ruption the whole distance, from the Hudson to the Potomac, and 

 indeed to far more distant limits in both directions. 



The theoretical discussion of the interesting problem, the cause 

 of this truly curious general fact, would be out of place in a 

 work like the present, restricted, as it is, to the description of a 

 comparatively small tract of the extensive region over which 

 this phenomenon prevails. But a hope is cherished, of my being 

 able at some future day, to connect it with views concerning the 

 elevation of our primary chain and the neighbouring axes, sus- 

 tained by facts, and a train of reasoning which may afford, 

 perhaps, a satisfactory solution of this apparently obscure enigma. 



The occurrence of workable roofing slates, is connected with 

 the presence of these cleavage planes. Hitherto they have been 

 discovered only in the belt which ranges near the base of the Blue 

 Mountain, having never been found of sufficient purity but in the 

 vicinity of the Delaware river, near the Water Gap. 



The largest quarry is on the west side of the river, in Penn- 

 sylvania ; a smaller one, yielding both roofing and writing slates of 

 excellent quality, lies nearly opposite, on the eastern side of the 

 river, in New Jersey. In both of these quarries, the true dip of 

 the rock is towards the west-northwest, at an angle of about 30°. 



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