re_ ancient
than the elevation of the most recent of the old coast lines,--perhaps
greatly less so. Meeting with an intelligent citizen of Wick, Mr. John
Cleghorn, I requested him to keep a vigilant eye on the shells, and to
ascertain for me, when opportunity offered, whether they occurred deep
in the deposit, or were restricted to merely the base of its exposed
front. On my return from Orkney, he kindly brought me a small collection
of fragments, exclusively, so far as I could judge, of _Cyprina
islandica_, picked up in fresh sections of the clay; at the same time
expressing his belief that they really belonged to the deposit as such,
and were not accidental introductions into it from the adjacent shore.
And at this point for nearly two years the matter rested, when my
attention was again called to it by finding, in the publication of Mr.
Keith Johnston's admirable Geological Map of the British Islands, edited
by Professor Edward Forbes, that other eyes than mine had detected
shells in the boulder-clay of Caithness. "Cliffs of Pleistocene," says
the Professor, in one of his notes attached to the map, "occur at Wick,
containing boreal shells, especially _Astarte borealis_."

I had seen the boulder-clay characteristically developed in the
neighborhood of Thurso; but, during a rather hurried visit, had lacked
time to examine it. The omission mattered the less, however, as my
friend Mr. Robert Dick is resident in the locality; and there are few
men who examine more carefully or more perseveringly than he, or who can
enjoy with higher relish the sweets of scientific research. I wrote him
regarding Professor Forbes's decision on the boulder-clay of Wick and
its shells; urging him to ascertain whether the boulder-clay of Thurso
had not its shells also. And almost by return of post I received from
him, in reply, a little packet of comminuted shells, dug out of a
deposit of the boulder-clay, laid open by the river Thorsa, a full mile
from the sea, and from eighty to a hundred feet over its level. He had
detected minute fragments of shell in the clay about a twelvemonth
before; but a skepticism somewhat similar to my own, added to the dread
of being deceived by mere surface shells, recently derived from the
shore in the character _of_ shell-sand, or of the edible species carried
inland for food, and then transferred from the ash-pit to the fields,
had not only prevented him from following up the discovery, but even
from thinking