236 



November 13, 1865. 



By Professor Sedgwick, F.R.S., "A Sketch of the Geology of the 

 Valley of Dent, with some account of a destructive Avalanche which 

 fell in the year 1752." 



The valley of Dent lies in the north-west corner of Yorkshire, 

 which is thrust in between Westmoreland and Lancashire, beyond 

 the natural limits of the county. The upper part of the valley is 

 excavated in the carboniferous groups which are continued south- 

 wards into Nottinghamshire, and northwards into Durham and 

 Northumberland, and through the greatest part of their range form 

 the watershed between the east and west coasts of England. All 

 the valleys that drain down to the Lune are partly formed in rocks 

 of the carboniferous age. In the upper part of Dent Dale, which is 

 one of these tributaries, the great scar-limestone appears only near 

 the bottom of the valley, while the sides are formed of soft shale 

 alternating with harder bands of sandstone and limestone ; and the 

 whole series is capped by mill-stone grit. The rainfall in some por- 

 tions of the Lake mountains is not less than 150 or 160 inches in the 

 year. Among the neighbouring carboniferous mountains the rain- 

 fall is much less ; but still it is at least three times the English 

 average ; and the winter fall of snow is in some years enormous. 

 Hence the becks, or mountain- streams, are often greatly swollen, and 

 the gills, or lateral branches, frequently descend in brawling torrents 

 from the mountain- side into the lower valley through deep ravines 

 and lateral valleys that have been excavated out of the shales and 

 sandstones in the course of past ages. On rare occasions a great fall of 

 snow, accompanied by a violent wind, will almost fill up the ravines 

 and lateral valleys, and form a dam across the descending water ; 

 and should there be a sudden thaw afterwards, the descending gills 

 may be held up for a while till the pressure of the water drives down 

 the barrier, and an avalanche is formed of mingled snow and water 

 (provincially called a brack), which rushes down with the roar of 

 thunder, and bears all before it into the beck below. On the 6th 

 of February, 1752, a very large one fell, destroying several houses 

 and farm buildings, and killing seven people, besides several head of 

 cattle. The following letter, written by an eye-witness, describes 

 the catastrophe (the spelling and punctuation have been slightly 

 modernized) : — 



" Harbourgill, 6th of the 2nd month, 1752. 



" DearBro' and Sister, — 



" These few lines I hope will find excuse : for it's not without a 

 cause that I have written no sooner to you. I fully purposed to 

 have seen you a considerable time since : but now, as things are at 

 present, I have lost all hopes of coming. Yet through the good provi- 

 dence of Heaven we are all alive and pretty well in health : which 

 is more than could be well expected, considering what dismal times 

 it has been with us in Dent. I hope I shall never live to see the like 

 again : for we had the greatest storm of wind and snow that conti- 



