él 
side. Mr. Hyatt also gave the details of several other 
observations. 
Mr. CoLLINGwoopD made some remarks on the effect of 
forests on the pressure of the air, and on the amount of rain, 
and on the dangerous results arising, in this latter respect, 
from the remoyal of woods. 
THE CHAIRMAN observed that in regard to the effect of 
denuding a country of wood, a serious error prevails. The 
belief that it produces a diminution in the amount of the 
rain-fall, is: by no means well established. There seems to 
be a conflict of opinion, and even of evidence on the subject. 
While in some instances such a reduction is very positively 
alleged to have taken place, in many others this result has - 
not been observed. 
Some very important effects of a different kind, however, 
are quite unquestionable. When the mountain summits 
have been robbed of their wood, the soil upon the upper 
slopes, deprived of the support furnished it by the roots of 
the trees, is no longer able to maintain its place, and is 
washed ‘down into the valleys below. These are then some- 
times overwhelmed by a deluge of sand and gravel, which 
covers up completely the fertile plains of the lower districts, 
and renders them unfit for cultivation. Mr. George P. 
Marsh, in his valuable work upon “Man and Nature,” re- 
counts some very destructive instances of this effect among 
the Alpine valleys of South-eastern France. The mountain 
summits, thus stripped of their soil, become barren slopes of 
rock, down which the water rushes with rapidity and violence. 
In the next place, the smaller rivers undergo a change of 
the most serious kind. They lose their sustained and equal 
flow, and become altogether irregular. The rain of a sum- 
mer’s shower drains rapidly from the precipitous and rocky 
heights which are no longer covered by asoil. It fills the 
bed of the stream, overflows it, and passes off in a torrent to 
the sea, leaving the stream shrunken and insignificant, till 
another storm of rain creates another inundation. Thus 
