nge dans cette espece de rocher." It is not necessary,
in the formation of a vein, that it should proceed in traversing all the
strata which then are superincumbent; it is reasonable to suppose, and
consistent with observation to find them stop short in proceeding from
one stratum to another. Had M. Schreiber found any pieces of the vein
contained in the calcareous rock, he would have had good reason for
that assertion; but, to conclude that fact from grounds which do not
necessarily imply it, is not to be permitted in sound reasoning, if
certainty is the object, and not mere probability.

SECT. II.--The Theory confirmed from Observations made on purpose to
elucidate the subject.

Having got a distinct view of the primary and secondary mineral bodies
or strata of the globe, and having thus acquired a particular object to
inquire after, with a view to investigate or illustrate this piece of
natural history, I was considering where we might most probably succeed
in finding the junction of the low country strata and alpine schistus.
I inquired of Mr Hall of Whitehall, who had frequent opportunities of
traversing those mountains which lie between his house in the Merse and
Edinburgh; and I particularly entreated him to examine the bed of the
Whittater, which he executed to my satisfaction.

Mr Hall having had occasion to examine the Pease and Tour burns, in
planning and superintending the great improvement of the post road upon
Sir James Hall's estate while Sir James was abroad, he informed me that
the junction of the schistus and sand-stone strata was to be found in
the Tour burn. Professor Playfair and I had been intending a visit to
Sir James Hall at Dunglass; and this was a motive, not so much to hasten
our visit, as to chose the most proper time for a mineral expedition
both upon the hills and along the sea shore.

It was late in the spring 1788 when Sir James left town, and Mr Playfair
and I went to Dunglass about the beginning of June. We had exceeding
favourable weather during the most part of our expedition; and I now
propose to give an account of the result of our observations.

Dunglass burn is the boundary between the counties of East Lothian and
Berwickshire; and it is almost the boundary between the vertical and
horizontal strata. To the north-west of this burn and beautiful dean are
situated the coal, lime-stone, marl, and sand-stone strata; they are
found stretching away along the shore in a very horiz