158 
Larch 2,142, White Cedar, Queensland, 2,105; the blue 
gum, therefore, takes a high position. 
That drying is an important element in the removal of 
th e causes of malaria cannot be doubted in the most of cases, 
but it is by no means apparent in all. It cannot be doubted 
that Garibaldi's plan of having another passage for the Tiber 
south of Rome would be of great advantage, but especially to 
the city itself, which is so frequently inundated, and which 
must, therefore, be on a foundation exceptionally wet. The 
mud brought down is proverbially great ; but so far as I 
could judge it was not so fine as that of the Nile, which, 
however, I have seen only in bottles. The Egyptian mud 
causes no fevers ; perhaps because it is more rapidly dried 
up. The mud of the Tiber is deposited on a very deep soil, 
but the same occurs on the Nile. The depth of mud, how- 
ever, may have an important bearing in a less burning sun. 
The mud of the Tiber seems always to have been remark- 
able, and one wonders why it should be able to go on so 
long unchanged, but on going up the river the difficulty 
ceases; there we find mud hills, many of them conical, all 
with steep sides and nearly all without any vegetation except 
below in some cases. There is in fact from water an enor- 
mous deposit raised to a great depth, and enough to keep the 
Tiber as muddy as ever for ages. It seemed to me that all 
this fine earth would be very valuable in much of our 
country, where we are glad of a few inches over chalk, or of 
a little soil scattered among large stones. Here it lies in 
great excess, cut into millions of little valleys, a fine study 
for those who wish to examine the action of streams, but a 
land wasted and almost useless. If these were made to bring 
out crops there is room enough for a great population to live, 
and if crops were closely grown, the mud would proportion- 
ately cease to flow. There is a good deal of friendfy inter- 
change of favours to be made between the lower and upper 
Tiber. That this is possible seems to be proved from 
