184 OBSERVATIONS ON THE FALL OF RAIN. 
heavy. Half the quantity which then fell in ten 
days has not unfrequently fallen in one. The 
greatest volume of the water was about 250 cubic 
feet per second, the mean 983. 
On the 17th, 22nd, and 27th of the same month, 
no rain having fallen since the 10th, the river 
was again carefully measured, as well as every 
separate stream which flowed into it. ‘There was 
but little difference in the results. The quan- 
tity gradually decreased, but not considerably. 
The natural stream at Dunscar weir, unassisted 
by artificial means, was about three cubic feet 
per second. 
The district from which these streams derive 
their source adjoins the land which supplies the 
Turton and Entwistle reservoir. It lies to the 
westward of the valley in which that reservoir is 
situated, and forms the first trough of any import- 
ance in the range of hills, which, commencing at 
Rivington Pike, and extending inland, is the first 
to break the clouds borne by the westerly winds, 
surcharged with moisture, from the Irish Sea. 
The external features and geological character of 
both districts are the same. Both are situated 
on the lower portion of the coal measure formation, 
