400 . PROFESSOR GEIKIE ON THE 
red shale, not unlike some of the shales or “ marls” of the lower red parts of the 
Caithness Old Red Sandstone. A similar, perhaps the same, bamd occurs on 
the west side of the Ham anticline at Kerry Goe. Thin bedded fingstones and 
shales succeed and continue to occupy the shore as far as St John’s Point. In 
no part of Caithness can the characteristic features of the upper flagstones be 
more conveniently studied than on this shore. The thinness of the layers, and 
their alternations of harder and softer texture, give rise to numerous parallel 
shore-reefs and ledges. A prevailing bright or cream-yellow crust, graduating 
into a greenish or even pinkish tint, is superinduced upon the strata by weather- 
ing, but when broken they are found to show the usual smoke-grey to brown 
tint. They consist of well-bedded fissile flagstones, often very shaly, and with 
partings of green shale. Many of them are so calcareous that, if found in the 
Scottish coal-fields, they would receive the name of “ calmy ” (pale argillaceous) 
limestones. The resemblance which, as already mentioned, they bear to some of 
the so-called fresh-water limestones and cement-stones at the base of the carbon- 
iferous system of the south of Scotland, cannot but strike any one who is 
familiar with the latter strata. This likeness includes not only the composition, 
colour, and mode of weathering, but even the minute wavy lamination indica- 
tive of intermittent but tranquil deposit. Other shaly layers are strongly 
pyritous. The bituminous impregnation already referred to is likewise well 
shown on this part of the coast. A shale, for example, near Barrogill Castle 
was found by Dr Hormayn to contain 30 per cent. of volatile matter, and to 
yield on an average 7500 cubic centimetres of a very luminous gas from 100 
grammes of the rock.* So large is the quantity of bituminous matter diffused 
through some portions of the group that it may be perceived, not only in specks 
and kernels, but even in black, soft, tar-like exudations from the joimts.t 
Another characteristic feature among these flagstones is well displayed along — 
the shores of the Pentland Firth—the occurrence of abundant sandy and 
calcareous concretions, varying in size from mere pea-like spherules up to 
masses five or six inches in diameter. These often roughen the sheets of flag- 
stone with their projecting surfaces, and, where large in size, give a kind of 
rudely honeycombed aspect to the rock in which they occur. In some of the 
Orkney flagstones similar concretions occur. In Rowsay, for example, they 
weather out, leaving casts so exactly resembling footprints that specimens have 
actually been sent to me as the “footprints of men, women, children, and 
animals.” 
Remains of plants occur more or less abundantly diffused through the flag- 
stones on this coast. ‘They are particularly observable at Mey, where the thin 
flagstones have long been quarried. Scales, teeth, plates, and other fragments 
* “Quart. Journ. Geol. Soc.” xv. 402. 
t This was noticed by Sxpewick and Murcutson, “Geol. Trans.” 2d ser, vol. iii. p. 134, 

