For a full and clear comprehension of this subject, it will be necessary to glance at the physical and geographical features of the district and to trace their relation and bearing to the surrounding country. In treating of this branch of the subject, our attention will be principally directed to that part lying between Burnley and Littleborough on one side, and Todmorden on the other—a district embracing the deep valleys of Cliviger and Walsden, in which are contained the two lowest watersheds in the whole of this central range of hills.
If, then, we take Todmorden as the central point of the district, from which to commence our observations, we shall find that that town is situated almost on a line with the highest summits of the Pennine Hills, in a deep gorge at the junction of the two streams which flow through the two defiles already mentioned, and on the main axis of that series of dislocations known as the great Pennine fault, which run in a line roughly coincident with the Walsden and Cliviger valleys, and the effect of which has been, not only to fracture and break up the rocks to a marvellous extent, but also to cause a reversal in the dip of the strata, those on the east dipping at an angle of about 5° to the S.E., and those to the west declining at an angle of from 20° to 45° to the W.S.W.
Starting from this centre, three valleys radiate in different directions, in lines almost equidistant from each other:—one stretching off through Walsden to Littleborough for a space of about 5 miles in a direction a little W. of S.; another taking a N.W. course through the sinuous gorge of Cliviger to Burnley, a distance of about 8 miles; whilst the third, the valley of the Calder, takes an E.N.E. direction.
The appearance thus presented, when traced on a geological map, reminds one forcibly of the device which characterizes the Manx copper coinage. By an examination of these arms, we shall find that they are three deep, narrow, rocky, tortuous channels, hemmed in on every side by massive walls of rock, cut into at intervals along their course by the entrance of tributary streams.
The watersheds of the Walsden and Cliviger valleys are at a comparatively low level, that of the first having an altitude of 627 feet above sea-level, and being eaten into to a depth of 330 feet below the shoulder, or first platform bounding the valley[1]; whilst that of the second is crossed at an elevation of 768 feet, and is excavated to a depth below the immediate country of 475 feet, a depression which would be greatly increased if the summit-level of the surrounding hills were taken as the datum-line for measurement.
The valley of the Calder, which forms the line of drainage through which the waters of the aforesaid tributary valleys, from their junction at Todmorden, pass off to the German Ocean, is cut in to a depth considerably in excess of those already described.
If, then, we view these valleys in relation to the initial period of their formation, structure, and physical characters, the total absence of drift or other indication of ice-action within their boundaries, or the marked contrast presented in the configuration of these and other
- ↑ Prof. Hull, Geol. Mag. vol. iii. p. 475.
