1!'
10
Wliich naturally increafe the furfacc of the delta formed with two of its principal branches,
and confequently adds to its projedion.
Thefe obfervations were aftcnvards corroborated and improved by a continuation of
the remarks which I made in a voyage on tlie P6, from Txirin to Fcrrara, where I had fufficient
time to examine minutely the conf t ruaion as well as the different ftrata of the foil,
through which tliis beautifiol river has traced its bed, witli the velocity of its waters, &c.
Th e P6, which rifes amongft the Cottian Alps, or Alpcs Cottias, at the foot of Mont
Vifo, is the only river which croffes this cxtenfivc and fertile valley in its whole length,
which it does from caft to weft, and fcrves as a refervoir to receive the innumerable torrents
which fall from thofe piles of mountains with loud and irrefiilible impetuofity, and which,
after feveral windings, occalioned paitly by the projeaion of the lateral mountains, ruilies
into tlie Adriatic Sea nearly oppofite to its fource, at about three hundred and fixty miles
in a ftraight line from its mouth.
Sti-abo tlie liiftorian juftly compares this river to the Nile, their efFcas being nearly
nmilar, as it fervcs to fertihze and enrich an cxtenfivc and beautiful country by its inundations
(which arc alfo neariy periodical), in fpite of the ravages it frequently makes in the
provinces of Bologna, Ferrara, &c. Vide the fifth book of Strabo's Ancicnt Geography.
Owing to the extreme vai-iations in the velocity of the waters of the P6, which is naturally
caufed by the declivity of its bed being more or lefs precipitate, as alfo from the
difference of the foil of which its bed is compofed, I have been led to imagine that the extenfive
valley of Lombardy may be divided into three di f t ina heads or parts, viz. upper,
middle, and lower.
Having alfo obferved, that the rapidity of this river diminiihes confiderably from tlie
city of Cremona to the fea, I was defirous of afcertaining its degree of velocity; and as in
moft flat countries the level of the beds of rivers is generally in the fame proportion as the
furface of the places thi'ough which they flow, I made ufe of iny barometer, conf t ruaed on
Monf . de Luc's plan, to certify the elevation of this city above the level of the fea, which I
accordingly ef feaed at different places with the greateft accuracy, and in the following
manner, viz. having taken a medium between the produce of my operations, I found
that Cremona was one hundred and five feet feven inches above die level of the f e a : its
diftance from the mouth of the Po in the Gulph of Venice Ijeing alfo about one hundred
and twenty Engl i ih miles, taken in a ftraight Jine, or fix hundred and thiity-thrce tlioufand
fix hundred feet, I confequently concluded that the declivity of the bed of the P6 is ncai'ly
equal to one foot on fix tlioufand, which is a vco' confiderable difference from what I had
obfer.-cd a few dnys prior to this, viz. from the town of Veraa to Cremona. As the diftance
from Verua to the fea (which is fituated on a hill on the fide of the P6) is neariy as far
again as Cremona, being about t%vo hundred and forty-fix miles, taken in a di r e a line, or
0.1C million two hundred and ninety-eight thoufand eight Jiundred and eighty feet, from
the gulph; but as this town is fix hundred and fifteen feet above the level of the fea, or
almoft fix times more elevated than Cremona, it is clear that the rapidity of the P6 mnft be
proportionally greater.
Having in my laii voyage to I l . ly confulled the ingcn.o™ Pi re l e c chi , a jefui l of Mi -
lan, relative to the remark, and notes I had juf t made, Iwa s happy to £nd that he not only
approved of them, but that he thought them as aeentate as the extent of fo large a eountry
would admit.
The approbation of fo able and feientifie a jndge flattered me not a little, and I thought
myfelf fortnnate in having eonfdted him, partienlarly as he had been ta m s intruHed
^ . th the exeention of the great hydraoKe works erefled on the eonfines of Ferrara and
Bologna, to prevent the ravages fo frequently o e c aWe d by the ovetflovving of the P3.
Th e vaft differenee in the velodty of thofe waters, added to tl.at of the foil through
whteh tl,is extenfive river „ n s from Verua to Cremona, and from tlrenoe to the fea as
before obferved, has indtteed me to fix on Verua as the boundary of the middle valley, atrd
Cremona as that of the lower one.
The foil of Cremona appears to be of modem formation, and feems to have been totally
formed by the immenfe aeeumula.ions or fediments of earth, flones, fand, &e. depof.ted by
theP6. As,eonvinei„gpr„ofofthiseonjea„re,thebare or lowefi ftratum ofthefoil is
entirely eompofed of pebbles or fmaU ftones of different forts and ft.es, whieh are readily
di f l ingui f ted to be mo i l y fragments or detaehed pieees of g „ „ i t e , quar t . , grey-roek f lone
eompounded of glimmer and quart . , fobifc.s, whieh have aequired that fl.pe and
pohfh from the extreme friffion and ineeffant rolhng whieh they experienee from the impetttofity
of the wa ter , whieh hurl them with fueh rapidity from the heights of thofe tremendous
inoimtaius.
On the tatnm of pebbles, whieh appear thiek, lies another of pebbles and fand
OF a out two feet o n l . Th e eolour of the fand varies, but the gram is nearly every where
the fame t ^ t t s both fine and fl.ining, refe.nbling partieles of miea and q u a r t , mixed