I Have not been able to trace the exact relationships of this zone, with its bands of limestone, to those already given, as underlying it. Certain grits and quartzites occurring on the top of the Ben Lawers ridge may possibly belong to it, and it is certain that many of the quartzites and grits of Glenlyon, Blair Athole, and Ben Y Ghloe belong to a horizon higher than the upper argillaceous series just described. Leaving the matter thus in the meantime, until further research shall explain their true relationship, it is certain that an arenaceous band of grits and quartzites succeeds the sericite and graphite schists of the upper argillaceous zone, thus completing the whole cycle of deposits, though no evidence has yet been forthcoming to show what or where the top of this series may be.