232 
TROPICAL NATURE 
i 
permanent springs to supply them are worthless. In the 
colder parts of the temperate zones the absence of forests is 
not so much felt, because the hills and uplands are naturally 
clothed with a thick coating of turf or peat which absorbs 
moisture and does not become overheated by the sun’s rays, 
and the rains are seldom violent enough to strip this protect- 
ive covering from the surface. In tropical and even in 
warm -temperate countries, on the other hand, the rains are 
periodical and often of excessive violence for a short period ; 
and when the forests are cleared away the torrents of rain 
soon strip off the vegetable soil, and thus destroy in a few 
years the fertility which has been the growth of many cen- 
turies. The bare subsoil becoming heated by the sun, every 
particle of moisture which does not flow off is evaporated, and 
this again reacts on the climate, producing long -continued 
droughts only relieved by sudden and violent storms, which 
add to the destruction and render all attempts at cultivation 
unavailing. Wide tracts of fertile land in the south of Europe 
have been devastated in this manner, and have become abso- 
lutely uninhabitable. Knowingly to produce such disastrous 
results would be a far more serious offence than any destruc- 
tion of property which human labour has produced and can 
replace ; yet we have ignorantly allowed such extensive clear- 
ings for coffee cultivation in India and Ceylon as to cause 
the destruction of much fertile soil, which human labour 
cannot replace, and which will surely, if not checked in time, 
lead to the deterioration of the climate and the permanent 
impoverishment of the country . 1 
Short Twilight of the Equatorial Zone 
One of the phenomena which markedly distinguish the 
equatorial from the temperate and polar zones is the 
shortness of the twilight and consequent rapid transition 
from day to night and from night to day, As this depends 
only on the fact of the sun descending vertically instead 
of obliquely below the horizon, the difference is most 
marked when we compare our midsummer twilight with 
1 For a terrible picture of the irreparable devastation caused by the reckless 
clearing of forests, see the third chapter of Mr. Marsh’s work, The Earth as 
Modified by Human Action. 
