The late eminent palæontologist, Mr. Salter, F.G.S., characterized the portion of the lovely valley of the Mawddach, at, and near the Falls of the Cain and Mawddach Rivers, "a perfect geological puzzle."

Certain it is, that touching Tyddyngwladus, the survey maps are greatly at fault; and, that the rocks, thereabouts, most of them, are of precambrian age.

Dr. Hicks, F.G.S., has hit upon the truth, approximately, I think, in what he calls Dimetian at St. David's, (as applied to the lowest beds of this district.)

After more than a year's unceasing investigation of these puzzling rocks and their associated minerals (chiefly with reference to the modes of occurrence of the "precious metals").