THE PARISH OF HALIFAX. XI. 



the extreme west of the parish, and successively to pass under 

 the outcrop of the newer and overlying members in proceed- 

 ing eastwards. The dip is considerable, about one in twenty, 

 and is accurately represented by the slope on which the greater 

 part of Halifax is built. For in fact the eastward slope of 

 nearly all the moors is the actual dip of the strata. As soon 

 as the western boundary is passed, as it practically coincides 

 with the axis of the anticlinal, the strata dip rapidly to the 

 west, so much so that the Lower Coal Measures, which are 

 nine miles to the east of Blackstone Edge or Widdop, reappear 

 in Lancashire within a mile or two. Perhaps the chief 

 botanical interest of this lies in the consequence that this 

 western encarpment is fully exposed to the prevailing winds, 

 which are now-a-days laden with the smoke from the south 

 Lancashire coalfield . This has probably caused the extinction 

 of two or three rare plants which will be mentioned later. 



The river Calder, especially if we consider the Hebden and 

 Gorple to be the main source above Hebden Bridge, 



instead of the stream passing through 

 Consequent Todmorden, flows in the direction of the dip, 

 Streams. being consequent upon the uplift of the strata. 



It has carved out its valley by erosion, aided by 

 the weathering of the sides, so that above Hebden Bridge it has 

 cut into and exposed the Yoredale rocks underlying the rocks at 

 the surface. Its fall from Todmorden to Brighouse is tolerably 

 uniform, and equal to not more than twelve feet per mile. This, 

 of course, is very much less than the actual dip of the rocks, so 

 that as it flows east it successively passes over the newer rocks. 

 At any point in its valley, however, the strata on either side 

 are identical, the cross section being symmetrical. 



Some of the tributaries of the Calder have the same 

 characters, flowing in the direction of the dip. This is notably 

 the case with the Red Beck in Shibden, though its course is 

 more southerly, as is the dip there. The upper courses of the 

 Ryburn, the middle portions of Luddenden Brook and of the 

 Hebble flow eastwards along the dip. 



But in most cases the tributaries run at right angles to the 

 main stream, originating subsequently along the strike of the 



strata. It follows therefore that a cross section 

 Subsequent in their valleys is not symmetrical, but the strata 

 Streams. on the western side, possessing a gentle slope, 



pass under those on the east, the outcrop of 

 which forms a steep escarpment. This is best seen in the 



