But it is with the difficulty itself we are now concerned, and not with the authorship. I. First then, suppose any statement, direct or indirect, had occurred in any Greek or Roman writer of the time--Cæsar, Tacitus, Dion Cassius, or Ptolemy--affirming, or even implying, such a level in the Clyde at the date in question, notwithstanding the Roman Wall, would the testimony of such authors have been rejected? If not, how would our geologists have disposed of it? or how would they have reconciled it with existing matters of fact? One can imagine the jealousy with which such texts would have been criticised; the assiduity with which every crevice on the coast would have been surveyed, not to contradict but to confirm them; and the fertility of invention with which theories would have been multiplied to harmonise them. Strange as it may appear, however, facts and statements amounting very nearly to this do occur, and have hitherto been overlooked, or purposely omitted in silence. The Roman Wall, for example, stops short with a town at Balmulzie on one side of the Kelvin, and begins again with another town at Simmerton, nearly a mile distant, on the opposite side of the Kelvin; but why should such a gap be there, if the Kelvin, which flows between, had not been something like a fiord at the moment? Again, it is distinctly affirmed by Herodian that the marshes of Clydesdale south of the Wall were constantly--end of the third, or beginning of the fourth century--emitting vapours which obscured the sky. But how could this be the case, if volcanic heat had not already been operating underneath, and the waters of the frith were then beginning to subside from their original higher levels?