294 
REVIEW. 
summer, and be at tlieir best in the following autumn. To 
the causes just referred to must be attributed the complaints 
of old millers, who depend chiefly or entirely on water, that 
they have a more frequent alternation of flush and slack 
water now to contend with than they did, both of which are 
harmful to them. 
There can be no doubt that there is less evaporation from 
well drained land than from undrained; also that there is 
more percolation into it. If more water goes in because 
more has been drained out, the same amount of water reaches 
the main streams, and as to whether it tends to produce 
floods or not is a question of time only. The difference 
between the evaporation from undrained and drained lands is 
a direct and considerable gain of water which, sometime, 
must find its way into the valley. To this quantity must be 
added or subtracted any water that would be arrested in its 
downward passage to a water-bearing bed, as a cause affecting 
flood and slack water, if it be allowed that drainage is chiefly 
operative during flood periods. 
What has been said about agricultural drainage does not 
materially affect the question as to whether the floods of 
recent years, in the Nen valley, were more violent or more 
frequent because of more efficient or more extensive drainage 
—the main cause we all know was excessive rainfall—but 
refers chiefly to the broader one as to whether floods are at 
any time increased by land drainage. 
The mcim object of the preceding remarks on agricultural 
drainage is to show that a great quantity of water is allowed 
to run away and help to produce floods. This water with a 
little extra trouble might often be made to feed the porous 
beds of the district, as I have proposed to feed the marlstone, 
and so be of immense benefit for the supply of villages 
throughout the summer, besides somewhat equalising the 
flow of the river. 
(To be continued.) 
e b i c to. 
The British Moss Flora. By JR. Braithwaite, M.D., F.L.S. Part XT. 
Fam. X., Grimmiacese I. Royal 8vo. 8s. L. Reeve and Co. 
This is the commencement of the second volume of Dr. Braitliwaite’s 
valuable work on the British Mosses, and is of special interest, as 
forming a complete monograph of the British species of Grimmia and 
its allies. The part is illustrated by eight plates, giving not only a 
life-size illustration of each plant, hut also magnified representations 
of all the various parts of each plant, all drawn with the singular 
