Isolated masses
of such faluns occur from near the mouth of the Loire, in the neighbourhood of
Nantes, to as far inland as a district south of Tours. They are also found at
Pontlevoy, on the Cher, about seventy miles above the junction of that river
with the Loire, and thirty miles south-east of Tours. Deposits of the same age
also appear under new mineral conditions near the towns of Dinan and Rennes, in
Brittany. I have visited all the localities above enumerated, and found the beds
on the Loire to consist principally of sand and marl, in which are shells and
corals, some entire, some rolled, and others in minute fragments. In certain
districts, as at Doue, in the Department of Maine and Loire, ten miles south-
west of Saumur, they form a soft building-stone, chiefly composed of an
aggregate of broken shells, bryozoa, corals, and echinoderms, united by a
calcareous cement; the whole mass being very like the Coralline Crag near
Aldborough, and Sudbourn in Suffolk. The scattered patches of faluns are of
slight thickness, rarely exceeding fifty feet; and between the district called
Sologne and the sea they repose on a great variety of older rocks; being seen to
rest successively upon gneiss, clay-slate, various secondary formations,
including the chalk; and, lastly, upon the upper fresh-water limestone of the
Parisian tertiary series, which, as before mentioned (Chapter 9), stretches
continuously from the basin of the Seine to that of the Loire.
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