sediment with which the waters
are charged is extremely fine, being derived from the destruction of
cliffs of red sandstone and shale, and as the tides rise fifty feet and
upwards, large areas are laid dry for nearly a fortnight between the
spring and neap tides. In this interval the mud is baked in summer by a
hot sun, so that it solidifies and becomes traversed by cracks, caused
by shrinkage. Portions of the hardened mud between these cracks may then
be taken up and removed without injury. On examining the edges of each
slab, we observe numerous layers, formed by successive tides, each layer
being usually very thin, sometimes only one-tenth of an inch thick. When
a shower of rain falls, the highest portion of the mud-covered flat is
usually too hard to receive any impressions; while that recently
uncovered by the tide near the water's edge is too soft. Between these
areas a zone occurs, almost as smooth and even as a looking-glass, on
which every drop forms a cavity of circular or oval form, and, if the
shower be transient, these pits retain their shape permanently, being
dried by the sun, and being then too firm to be effaced by the action of
the succeeding tide, which deposits upon them a new layer of mud. Hence
we often find, in splitting open a slab an inch or more thick, on the
upper surface of which the marks of recent rain occur, that an inferior
layer, deposited during some previous rise of the tide, exhibits on its
under side perfect casts of rain-prints, which stand out in relief, the
moulds of the same being seen on the layer below. But in some cases,
especially in the more sandy layers, the markings have been somewhat
blunted by the tide, and by several rain-prints having been joined into
one by a repetition of drops falling on the same spot; in which case the
casts present a very irregular and blistered appearance.

The finest examples which I have seen of these rain-prints were sent to
me by Dr. Webster, from Kentville, on the borders of the Bay of Mines,
in Nova Scotia. They were made by a heavy shower which fell on the 21st
of July, 1849, when the rise and fall of the tides were at their
maximum. The impressions (see fig. 13) consist of cup-shaped or
hemispherical cavities, the average size of which is from one-eighth to
one-tenth of an inch across, but the largest are fully half an inch in
diameter, and one-tenth of an inch deep. The depth is chiefly below the
general surface or plane of stratification