GEOLOGY OF SOME OF THE RIVER-SCENERY OF DERBYSHIRE. I 57 



giving us the beautiful scenery of " the Vale " between the High 

 Tor and Masson. Near Cromford the river quits the limestone 

 and again enters the Yoredale shales. A glance at a geological 

 map of the district will show that it was, so to speak, wholly 

 unnecessary for the river to cut through the limestone at all. 

 When it reached the limestone, had it turned but the slightest 

 distance to one side (the east), it could have continued to flow 

 through soft shales to Cromford. It is recorded that originally 

 the gorge where the river enters the limestone was only just 

 broad enough to admit the river, and that it had to be widened 

 by blasting when the highway was made along the valley. 

 Strange as these facts may appear, all difficulty vanishes in a 

 moment if we suppose that the birth of the Derwent dates back to 

 a time before the Yoredale shales, in the direction of Rowsley 

 and the carboniferous limestone of Matlock presented to view the 

 difference of altitude which we now observe. Doubtless at one 

 time the surface of the whole country was a plain as high as the 

 highest portion of the carboniferous limestone at Matlock. It 

 was at this period that the Derwent began to flow. The 

 Yoredale shales of Rowsley being then as high as the now 

 towering carboniferous limestone of Matlock, when the river 

 had flowed across the one, the other presented no such rocky wall 

 as we now behold. Without any necessity for turning aside to 

 escape obstructions, the river then ran on its even course, the 

 only change being in the character of the strata forming the river- 

 bed. As, however, the river deepened its channel the atmospheric 

 agencies would act with unequal rapidity on the strata flanking the 

 river at various parts of its course. The soft Yoredale shales 

 would rapidly suffer disintegration, and allow a wide open river 

 valley to be scooped out of them, as shown in the woodcut. 

 The degraded materials would be washed down to the stream, and 

 carried away by it— thus the " area of drainage " would ever be 

 increasing. In short, as rapidly as the river deepened its channel 

 in the Yoredale shales, atmospheric agencies would wear away 

 and lower the general surface of the country on each side. The 

 carboniferous limestone on the other hand, being harder and more 



