the distant horizon. These mud flats were much frequented by birds
of the wader family, that used to come and fish in the shallow pools for
the small fry that had lingered behind when the tide fell; and my
cousin, a keen sportsman in his day, has told me that he used to steal
upon them in his mud shoes,--flat boards attached to the soles, like the
snow shoes of the higher latitudes,--and enjoy rare sport in knocking
down magnificent game, such as "the roseate spoonbill" and "gorgeous
flamingo." There were times, however, when the mud shoe proved of no
avail, and the flat expanse remained impassable for weeks,--

"A boggy syrtis, neither sea
Nor good dry land."

The coast,--directly impinged on by the drift current, and beaten by the
long roll of waves which had first begun to rise under the impulsions of
the trade winds on the African coast two thousand miles away,--was much
exposed to tempests; and after every fresh storm from the east, a huge
bank of mud used to come rolling in from the sea, three or four feet
abreast, and remain wholly impassable until, during some two or three
neap tides, its surface had been exposed to a tropical sun, and
partially consolidated by the heat. And then the waste would become
passable as before, and the chopped and broken surface, exposed to the
ordinary action of the sea, and to gradual depositions during flood,
would begin to be smoothed over, and the birds would find themselves no
longer safe. Now, I am inclined to think that we have here the
conditions necessary to the formation of the Thurso deposits. Let us
suppose, near where Thurso now stands, a wide tract of flat mud banks in
a sea so shallow as to be laid dry at ebb for miles together. Let us
further suppose periods of tranquil deposition or re-arrangement, during
which one ripple-marked stratum is laid quietly down over another, and
the fish, killed by accident, or left stranded by the evaporation of the
little pools, are covered up, like the plants in a botanist's
drying-book, in a state of complete entireness. Let us yet further
suppose great mud banks driven by occasional tempests from the deeper
water beyond, and so heaped up over these sedimentary beds as to be
exposed during even the flood of neap tides to the desiccating
influences of the atmosphere and the sun, until the surface has become
hard as a sun-burned brick, and has chopped into polygonal partings,
with wide rents between. And finally, let us supp