Action of Waves. 383 



the tides. The shallower parts of the lake are so 

 thickly grown in summer with aquatic weeds that 

 a boat can only be forced through them with the 

 utmost difficulty. Some of these grow in as much 

 as eight or even ten feet of water. Nearer the shore, 

 where it is marshy, the mare's-tail flourishes over 

 some acres : there is often a slight marshy odor here, 

 which increases as the foot presses the yielding 

 mud. 



When the water is low in autumn these are mown, 

 and, with the aquatic grasses at the edge and the 

 rushes, made into the roughest kind of hay imagin- 

 able. The coarser parts are used as litter ; the best 

 is mixed with fodder and eaten by cattle. Many 

 wagon loads are thus taken away, but as many 

 more remain ; and in walking over the spongy ground 

 a smart ' pop ' is continually heard : it is caused by 

 the sudden compression of air under the foot in the 

 mare's-tails lying about ; for their stems are hollow, 

 and have knots at regular intervals. 



After a continuance of the wind in one quarter 

 for a few days south or south-west the opposite 

 shores are lined with such weeds carried across, to- 

 gether with great quantities of dead branches fallen 

 from the trees and willows. So that on a small scale 

 the same thing happens as with the drift wood of 

 the ocean ; and, indeed, by studying the action of 

 natural forces as exhibited in our own pools and 

 brooks, it becomes much easier to comprehend the 

 gigantic operations by which the surface of the earth 

 is altered. 



For instance, the north-eastern edge of the water 

 is continually encroaching on the land, eating away 



