up consisting of beds deposited in the more central
parts of the basin, and towards the side farthest from the mountains.
The following characters would form the principal marks of distinction
between the strata in each series:--The more ancient system would be
composed, for the most part, of coarser materials, containing many beds
of pebbles and sand, often of great thickness, and sometimes dipping at
a considerable angle. These, with associated beds of finer ingredients,
would, if traced round the borders of the basin, be seen to vary greatly
in color and mineral composition, and would also be very irregular in
thickness. The beds, on the contrary, in the newer group, would consist
of finer particles, and would be horizontal, or very slightly inclined.
Their color and mineral composition would be very homogeneous throughout
large areas, and would differ from almost all the separate beds in the
older series.

The following causes would produce the diversity here alluded to between
the two great members of such lacustrine formations:--When the rivers
and torrents first reach the edge of the lake, the detritus washed down
by them from the adjoining heights sinks at once into deep water, all
the heavier pebbles and sand subsiding near the shore. The finer mud is
carried somewhat farther out, but not to the distance of many miles, for
the greater part may be seen, as, for example, where the Rhone enters
the Lake of Geneva, to fall down in clouds to the bottom, not far from
the river's mouth. Thus alluvial tracts are soon formed at the mouths of
every torrent and river, and many of these in the course of ages become
of considerable extent. Pebbles and sand are then transported farther
from the mountains; but in their passage they decrease in size by
attrition, and are in part converted into mud and sand. At length some
of the numerous deltas, which are all directed towards a common centre,
approach near to each other; those of adjoining torrents become united,
and each is merged, in its turn, in the delta of the largest river,
which advances most rapidly into the lake, and renders all the minor
streams, one after the other, its tributaries. The various mineral
ingredients of all are thus blended together into one homogeneous
mixture, and the sediment is poured out from a common channel into the
lake.

As the average size of the transported particles decreases, while the
force and volume of the main river augments, the newe