534 THE VAL DI CHIANA. 
fore small; it does not appear to have ever been divided into 
opposite slopes by a true watershed, and the position of the 
summit seems to have shifted according to the varying amount 
and place of deposit of the sediment brought down by the 
lateral streams which emptied into it. The length of its princi- 
pal channel of drainage, and even the direction of its flow at 
any given point, were therefore fluctuating. Hence, much dif- 
ference of opinion was entertained at different times with re- 
gard to the normal course of this stream, and, consequently, to 
the question whether it was to be regarded as properly an afilu- 
ent of the Tiber or of the Arno. 
The bed of the latter river at the bend has been eroded to 
the depth of thirty or forty feet, and that, apparently, at no 
very remote period.* If it were elevated to what was evidently 
its original height, the current of the Arno would be so much 
above that of the Paglia as to allow of a regular flow from its 
channel to the latter stream, through the Val di Chiana, pro- 
vided the bed of the valley had remained at the level which 
excayations prove it to have had a few centuries ago, before it 
was raised by the deposits I have mentioned. These facts, 
together with the testimony of ancient geographers which 
scarcely admits of any other explanation, are thought to prove 
that all the waters of the Upper Arno were originally dis- 
charged through the Val di Chiana into the Tiber, and that a 
part of them still continued to flow, at least occasionally, in 
that direction down to the days of the Roman empire, and per- 
haps for some time later. The depression of the bed of the 
Arno, and the raising of that of the valley by the deposits of 
the lateral torrents, finally cut off the branch of the river which 
had flowed to the Tiber, and ail its waters were turned into its 
present channel, though the drainage of the principal part of 
the Val di Chiana appears to have been in a south-eastwardly 
direction until within a comparatively recent period. 
* Able geologists infer from recent investigations, that, although the Arno 
flowed to the south within the pliocenic period, the direction of its course was 
changed at an earlier epoch than that supposed in the text. 
