The Ancient Fauna of Essex. 
9 
occupies. Every stream is converted by the Beavers into a 
series of falls with beaver-dams, and large, deep, clear, still 
pools of water. It is evident that, if ever a big flood 
came down such rivers, these beaver-dams would be quite 
calculated to cause an overflow and an inundation of the 
Forest for miles around. Many of the forest-trees could not 
stand this excessive damp, and would give way to Sphagnum 
or bog-moss ; and large tracts thus flooded would be converted 
into peaty, marshy fen-land. That I believe to be the origin 
of the fen-lands over a great part of our Eastern counties. Of 
course, geologically, there is another aspect of the question 
which we must not omit to mention ; that is, the strata in 
this area are of a soft clayey, chalky, or sandy character, and 
lend themselves admirably to the action of denuding agents : 
but I have no doubt that the Beaver helped these agents 
most effectively. By damming back the water of its streams 
it destroyed the Forest, and converted it by degrees into a 
primitive marsh . 7 
We must now pass from the consideration of the series of 
deposits characterised by the fauna nearest to that existing 
at the present day to those belonging to an earlier date, but 
which are also found in the valleys of the Thames, the Lea, 
and the Boding, and which underlie the more superficial 
deposits of which we have already spoken. They consist 
mainly of gravels, sands, and brick-earth, and are all of 
fluviatile origin, being marked by the presence of land and 
7 “ The flow of streams is sometimes interfered with, or even diverted by 
the operations of animals. Thus the Beaver, by cutting down trees 
(sometimes one foot or more in diameter) and constructing dams with 
the stems and branches, checks the flow of water-courses, intercepts 
floating materials, and sometimes even diverts the water into new 
channels. This action is typically displayed in Canada and in the 
Bocky Mountain regions of the United States. Thousands of acres in 
many valleys have been converted into lakes, which, intercepting the 
sediment carried down by the streams, and being likewise invaded by 
marshy vegetation, have subsequently become morass, and finally meadow- 
land. The extent to which, in these regions, the alluvial formations of 
valleys have been modified and extended by the operations of the Beaver 
is ahnost incredible ” (Geikie’s ‘ Geology,’ p. 455). See also ‘ The American 
Beaver and his Works,’ by Lewis H. Morgan, Philadelphia, 1868, 
