The survival of types is a recognised feature in the philosophy of geology. Long after their contemporaries have disappeared we find stray shells outliving catastrophe and change, and recalling the features of times which have passed away. Similarly we encounter in our historical inquiries, even if we choose for our guides the most patient and scrupulous of writers, errors that have survived a crushing exposure of many years' date. They linger about the sentences of fastidiously critical historians, the relics of an uncritical age, to the great delight of some simple-minded scholars, who for the first time in their lives discover the fallibility of their master.