north,--ascending in the system as I climbed the eminence, which forms here the central ridge of the old Maolbuie Common,--I spent some little time in a quarry of pale red sandstone, known, from the moory height on which it has been opened, as the quarry of the Maolbuie. But here, as elsewhere, the folds of that upper division of the Lower Old Red in which it has been excavated contain nothing organic. Why this should be so universally the case,--for in Caithness, Orkney, Cromarty, and Ross, wherever, in short, this member of the system is unequivocally developed, it is invariably barren of remains,--cannot, I suspect, be very satisfactorily explained. Fossils occur both over and under it, in rocks that seem as little favorable to their preservation; but during that intervening period which its blank strata represent, at least the _species_ of all the ichthyolites of the system seem to have changed, and, so far as is yet known, the _genus_ Coccosteus died out entirely. The Black Isle has been elaborately described in the last Statistical Account of the Parish of Avoch as comprising at least the analogues of three vast geologic systems. The Great Conglomerate, and the thick bed of coarse sandstone of corresponding character that lies over it, compose all which is not primary rock of that south-eastern ridge of the district which forms the shores of the Moray Frith; and _they_ are represented in the Account as Old Red Sandstone proper. Then, next in order,--forming the base of a parallel ridge,--come those sandstone and argillaceous bands to which the ichthyolite beds belong; and these though at the time the work appeared their existence in the locality could be but guessed at, are described as representatives of the Coal Measures. Last of all there occur those superior sandstones of the Lower Old Red formation in which the quarry of the Maolbuie has been opened, and which are largely developed in the central or _backbone_ ridge of the district. "And these," says the writer, "we have little hesitation in assigning to the _New_ Red, or variegated Sandstone formation." I remember that some thirteen years ago,--in part misled by authority, and in part really afraid to represent beds of such an enormous aggregate thickness as all belonging to one inconsiderable formation,--for such was the character of the Old Red Sandstone at the time,--I ventured, though hesitatingly, and with less of detail, on a somewhat similar statement regarding the sandstone deposits of the parish of Cromarty. But true it is, notwithstanding, that the stratified rocks of the Black Isle are composed generally, not of the analogues of three systems, but of merely a fractional portion of a single system,--a fact previously established in other parts of the district, and which my discovery of this day in the Burn of Killein served yet farther to confirm in relation to that middle portion of the tract in which the parish of Avoch is situated.