A Manual of Elementary Geology: or, The Ancient Changes of the Earth and its Inhabitants as Illustrated by Geological MonumentsLyell, Charles, Sir
Science
A Manual of Elementary Geology: or, The Ancient Changes of the Earth and its Inhabitants as Illustrated by Geological Monuments
Lyell, Charles, Sir
Geology
_Molasse of Switzerland._--If we cross the Alps, and pass from Piedmont
to Savoy, we find there, at the northern base of the great chain, and
throughout the lower country of Switzerland, a soft green sandstone much
resembling some of the beds of the basin of the Bormida, above
described, and associated in a similar manner with marls and
conglomerate. This formation is called in Switzerland "molasse," said to
be derived from "mol," "_soft_" because the stone is easily cut in the
quarry. It is of vast thickness, and probably divisible into several
formations. How large a portion of these belong to the Miocene period
cannot yet be determined, as fossil shells are often entirely wanting.
In some places a decided agreement of the fossil fishes of the molasse
and faluns has been observed. Among those common to both, M. Agassiz
pointed out to me _Lamna contortidens_, _Myliobates Studeri_, _Spherodus
cinctus_, _Notidanus primigenius_, and others.
_Lisbon._--Marine tertiary strata near Lisbon contain shells which agree
very closely with those of Bordeaux, and are therefore referred to the
Miocene era. Thus, out of 112 species collected by Mr. Smith of Jordanhill,
between 60 and 70 were found to be common to the strata of Bordeaux and
Dax, the recent species being in the proportion of 21 per cent.
_Older Pliocene and Miocene formations in the United States._--Between the
Alleghany mountains, formed of older rocks, and the Atlantic, there
intervenes, in the United States, a low region occupied principally by beds
of marl, clay, and sand, consisting of the cretaceous and tertiary
formations, and chiefly of the latter. The general elevation of this plain
bordering the Atlantic does not exceed 100 feet, although it is sometimes
several hundred feet high. Its width in the middle and southern states is
very commonly from 100 to 150 miles. It consists, in the South, as in
Georgia, Alabama, and South Carolina, almost exclusively of Eocene
deposits; but in North Carolina, Maryland, Virginia, and Delaware, more
modern strata predominate, which I have assimilated in age to the English
crag and Faluns of Touraine.[172-A] If, chronologically speaking, they can
be truly said to be the representatives of these two European formations,
they may range in age from the Older Pliocene to the Miocene epoch,
according to the classification of European strata adopted in this chapter.
The proportion of fossil shells agreeing with recent, out of 147 species
collected by me, amounted to about 17 per cent., or one-sixth of the
whole; but as the fossils so assimilated were almost always the same as
species now living in the neighbouring Atlantic, the number may
hereafter be augmented, when the recent fauna of that ocean is better
known. In different localities, also, the proportion of recent
species varied considerably.
[Illustration: Fig. 151. _Fulgur canaliculatus._ Maryland.]
[Illustration: Fig. 152. _Fusus quadricostatus_, Say. Maryland.]
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