THE MIDDLE LIAS OF NORTHAMPTONSHIRE 
263 
An increased rainfall in a district need not be a "’cause of 
floods, for, if it is not particularly heavy, a rain may continue 
a long time before any very perceptible effect is noticed, 
depending upon the previous condition of the ground. After 
a dry period two or three inches of rain may fall before there 
is sensible percolation, much less floods ; the huge cracks in 
even badly drained soils receiving and distributing a great 
quantity of water through the dry earth. At other times 
less than an inch of rain may produce considerable floods. 
In July, 1875, very extensive floods occurred in the 
Midland counties ; part of Northampton was under water, 
and the Nen valley was like one vast lake. The rains which 
caused these floods had been preceded by heavy rains a few 
days previously; and so the ground was well saturated, and 
made incapable of receiving much more water.* Other 
floods occurred later in the year, and altogether, perhaps, 
floods were more extensive and destructive than in any other 
year since 1852. 
On Thursday, April 16th, 1885, about 1*16 inches of rain 
(partly snow at first) fell in Northampton from mid-night to 
mid-day, and this fall produced heavy floods in the-Nen 
valley the same day, and lasting over the Sunday following. 
This had not been preceded by any exceptional rainfall. 
In May, 1886, no rain fell for the first nine days. On the 
10th there was '10 inches, on the 11th # 45 inches, and on the 
12tli 1-07 inches, in all l - 62 inches in three days, and heavy 
floods were out in the Nen valley on the 12th. Hence we see 
how small an amount of rain may produce floods when the 
predisposing circumstances have not been exceptional. 
Of course floods almost invariably follow the melting of 
snow, for although percolation is most easy at such times, 
owing to the disintegration of the ground by frost, it is gener¬ 
ally more or less saturated with water, and the amount of 
snow melted may be the accumulation of several separate snow¬ 
storms. It is not unusual for the thaw to be accompanied by 
rain, which still further increases the flood. To these causes 
may be added one other: if the snow fell after frost had set 
in, when the thaw comes much water will run off the surface 
and accumulate in the valleys before the ground has thawed 
sufficiently to let any in. 
According to the best information I can get, it appears 
that when a fall of rain occurs sufficient to cause a flood in 
* For much valuable information on these periods of heavy rain¬ 
fall see “ On the Floods in England and Wales during 1875, and on 
Water Economy,” by Geo. J. Symons. Paper read before the 
Institution of Civil Engineers, 1876. 
