, according to Saussure, stands
six feet lower. If, then, we could obtain a section of the accumulation
formed in the last eight centuries, we should see a great series of
strata, probably from 600 to 900 feet thick (the supposed original depth
of the head of the lake), and nearly two miles in length, inclined at a
very slight angle. In the mean time, a great number of smaller deltas
are growing around the borders of the lake, at the mouths of rapid
torrents, which pour in large masses of sand and pebbles. The body of
water in these torrents is too small to enable them to spread out the
transported matter over so extensive an area as the Rhone does. Thus,
for example, there is a depth of eighty fathoms within half a mile of
the shore, immediately opposite the great torrent which enters east of
Ripaille, so that the dip of the strata in that minor delta must be
about four times as great as those deposited by the main river at the
upper extremity of the lake.[337]

_Chronological computations of the age of deltas._--The capacity of this
basin being now ascertained, it would be an interesting subject of
inquiry, to determine in what number of years the Leman Lake will be
converted into dry land. It would not be very difficult to obtain the
elements for such a calculation, so as to approximate at least to the
quantity of time required for the accomplishment of the result. The
number of cubic feet of water annually discharged by the river into the
lake being estimated, experiments might be made in the winter and summer
months, to determine the proportion of matter held in suspension or in
chemical solution by the Rhone. It would be also necessary to allow for
the heavier matter drifted along at the bottom, which might be estimated
on hydrostatical principles, when the average size of the gravel and the
volume and velocity of the stream at different seasons were known.
Supposing all these observations to have been made, it would be more
easy to calculate the future than the former progress of the delta,
because it would be a laborious task to ascertain, with any degree of
precision, the original depth and extent of that part of the lake which
is already filled up. Even if this information were actually obtained by
borings, it would only enable us to approximate within a certain number
of centuries to the time when the Rhone began to form its present delta;
but this would not give us the date of the origin of the Leman Lake in