1852.] PRESTWICH ON THE HOLMFIRTH FLOOD. 227 



recently given an account. The object of the present communication 

 is merely to notice briefly a few facts bearing upon the geological 

 question, and having reference to the transporting power of water. 



The portion of the embankment destroyed extends to its full depth, 

 and forms a gap about 140 feet in width at top, and 25 feet at bottom. 

 The weight of the materials thus swept away, and scattered in gradually 

 decreasing quantity for a distance of half a mile, cannot be much less 

 than 40,000 to 50,000 tons. A large proportion, however, is de- 

 posited within the first 300 feet. At this point a stone-built mill, 

 two storeys high, was situated : all that portion of it in the way of 

 the flood-stream was at once swept down, and the site covered with 



6 to 10 feet of debris. As far as this the valley is very narrow, and 

 the action of the water on the slopes on its side tore up the surface 

 to a depth of 10 to 20 feet (forming a small cliff-like bank where it 

 had been a slope previously, see fig. 2), and carrying away large 

 masses of rock to considerable distances. It is to be observed, how- 

 ever, that the first rush of the waters out of the reservoir excavated 

 a circular pool in the old water-channel at the foot of the embank- 

 ment. The rock in this pass has a dip of about 5° nearly in a 

 direction down the valley, and consists of a pebbly quartzose conglo- 

 merate, of a character easily recognised. 



Just below the mill the valley opens out from a breadth of 30 to 

 50 yards to that of 100 to 200 yards, and the force of the flood 

 became necessarily much diminished ; still the meadows extending 

 from this point to Digley are almost entirely covered to a depth of 

 from 1 to 2 feet, with masses of rock mixed with sand and gravel, 

 derived from the embankment and the sides of the pass above-mea-. 

 tioned. The bulk of the debris scattered over the valley consists of 

 angular fragments of rock not exceeding 1 or 2 feet in diameter ; but 

 amongst them a few large rough blocks stand out in prominent relief. 

 As the portion of the outcrop of the rock exposed to the action of 

 the torrent was not large, the sides of the valley being much covered 

 with debris, these larger masses are not numerous. There are four 

 which particularly attract attention. One of these, a block measuring 



7 feet in extreme length by 5 feet in breadth, and 2^ feet in depth, and 

 weighing probably from 5 to 6 tons, has been transported a distance 

 of about half a mile, and now lies in the valley near Digley Mill. 

 There is near it another mass of about the same size. A third block, 

 rather nearer the reservoir, measures 12 feet by 6y, and 2 feet deep, 

 and may weigh 7 or 8 tons. The most remarkable block, however, 

 lies in the middle of the valley, near Upper Digley Mill, and at a di- 

 stance of a third of a mile from the parent rock ; it is 22 feet long, 

 6 feet broad, and 3|- feet thick, and probably weighs about 20 tons. 



Although the greater part of this portion of the valley is covered 

 with debris, there are places where its surface has been torn up to 

 the depth of from 4 to 5 feet. This also occasionally occurs in other 

 places lower down the valley, but generally the centre of the valley 

 has been covered with debris, which the denudation of the banks in 

 the narrower passes has furnished. In the middle of the open part 

 of the valley, above Upper Digley Mill, an old oak-tree still stands. 



