re, as some small matter may be perceived in that place. I know not
what species of substance this has been, whether saline or phlogistic,
but it must have had the power of either volatilising or changing the
ferruginous or red tinging substance so as to make it lose its colour.

I have only mentioned spherical spots for distinctness sake; but this
discharging operation is found diversifying those strata in various
ways, but always referable to the same or similar causes. Thus, in many
of the veins or natural cracks of those strata, we find the colour
discharged for a certain space within the strata; and we often see
several of those spots united, each of them having proceeded from its
own centre, and uniting where they approached. In the two veins above
mentioned, of whin-stone and spar traversing the strata, the colour of
the strata is, discharged more or less in the places contiguous with the
veins.

I am now to mention another appearance of a different kind. Those strata
of marl are in general not much consolidated; but among, them there
are sometimes found thin calcareous strata extremely consolidated,
consequently much divided by veins. It is in the solid parts of those
strata, perfectly disconnected from the veins, that there are frequent
cavities curiously lined with crystals of different sorts, generally
calcareous, sometimes containing also those that are siliceous, and
often accompanied with pyrites. I am persuaded that the origin of those
cavities may have been some hollow shells, such as _echini_ or some
marine object; but that calcareous body has been so changed, that it is
not now distinguishable; therefore, at present, I hold this opinion only
as conjecture.

Having, in my return to Edinburgh, traveled up the Tiviot, with a view
to investigate this subject of primary and secondary operations of the
earth, I found the vertical strata, or alpine schistus, in the bed of
the river about two miles below Hawick. This was the third time I had
seen those vertical bodies after leaving the mountains of Lauderdale.
The first place was the bed of the river Tweed, at the new bridge below
Melrose; but here no other covering is to be seen above those vertical
strata besides the soil or traveled earth which conceals every thing
except the rock in the bed of the river. The second place was Jedburgh,
where I found the vertical strata covered with the horizontal sandstone
and marl, as has been now described. The third pl