contain
either combustible or elastic matter."

This chapter ought not to be concluded without a short notice of that
remarkable rain known to geologists as "fossil rain." In the new
red-sandstone of the Storeton quarries, impressions of the foot-prints of
ancient animals have been discovered; and in examining some of the slabs
of stone extracted at the depth of above thirty feet, Mr. Cunningham
observed "that their under surface was thickly covered with minute
hemispherical projections, or casts in relief of circular pits, in the
immediately subjacent layers of clay. The origin of these marks, he is
of opinion, must be ascribed to showers of rain which fell upon an
argillaceous beach exposed by the retiring tide, and their preservation
to the filling up of the indentations by sand. On the same slabs are
impressions of the feet of small reptiles, which appear to have passed
over the clay previously to the shower, since the foot-marks are also
indented with circular pits, but to a less degree; and the difference Mr.
Cunningham explains by the pressure of the animal having rendered these
portions less easily acted upon." The preservation of these marks has
been explained by supposing dry sand, drifted by the wind, to have swept
over and filled up the footprints, rain-pits, and hollows of every kind,
which the soft argillaceous surface had received.

The frontispiece to the present chapter (p. 156), represents a slab of
sandstone containing impressions of the foot of a bird and of rain drops.
This slab is from a sandstone basin near Turner's Falls, a fine cataract
of the Connecticut river in the State of Massachusetts, and is described
by Dr. Deane in a recent number of the American Journal of Science. "It
is rare," says that gentleman, to "find a stratum containing these
footprints exactly as they were made by the animal, without having
suffered change. They are usually more or less disturbed or obliterated
by the too soft nature of the mud, the coarseness of the materials, and
by many other circumstances which we may easily see would deface them, so
that although the general form of the foot may be apparent, the minute
traces of its appendages are almost invariably lost. In general, except
in thick-toed species, we cannot discover the distinct evidences of the
structure of the toes, each toe appearing to be formed of a single joint,
and seldom terminated by a claw. But, a few specimens hitherto
discovered at thi