ow in progress.

_Targioni_, 1751.--Targioni, in his voluminous "Travels in Tuscany, 1751
and 1754," labored to fill up the sketch of the geology of that region
left by Steno sixty years before. Notwithstanding a want of arrangement
and condensation in his memoirs, they contained a rich store of faithful
observations. He has not indulged in many general views, but in regard
to the origin of valleys, he was opposed to the theory of Buffon, who
attributed them principally to submarine currents. The Tuscan naturalist
labored to show that both the larger and smaller valleys of the
Apennines were excavated by rivers and floods, caused by the bursting of
the barriers of lakes, after the retreat of the ocean. He also
maintained that the elephants and other quadrupeds, so frequent in the
lacustrine and alluvial deposits of Italy, had inhabited that peninsula;
and had not been transported thither, as some had conceived, by Hannibal
or the Romans, nor by what they were pleased to term "a catastrophe of
nature."

_Lehman_, 1756.--In the year 1756 the treatise of Lehman, a German
mineralogist, and director of the Prussian mines, appeared, who also
divided mountains into three classes: the first, those formed with the
world, and prior to the creation of animals, and which contained no
fragments of other rocks; the second class, those which resulted from
the partial destruction of the primary rocks by a general revolution;
and a third class, resulting from local revolutions, and in part from
the deluge of Noah.

A French translation of this work appeared in 1759, in the preface of
which, the translator displays very enlightened views respecting the
operations of earthquakes, as well as of the aqueous causes.[82]

_Gesner_, 1758.--In this year Gesner, the botanist, of Zurich,
published an excellent treatise on petrifactions, and the changes of the
earth which they testify.[83] After a detailed enumeration of the
various classes of fossils of the animal and vegetable kingdoms, and
remarks on the different states in which they are found petrified, he
considers the geological phenomena connected with them; observing, that
some, like those of OEningen, resembled the testacea, fish, and plants
indigenous in the neighboring region;[84] while some, such as ammonites,
gryphites, belemnites, and other shells, are either of unknown species,
or found only in the Indian and other distant seas. In order to
elucidate the structure of the earth,