But it would be difficult to overestimate the importance of evidence which forms a connecting link between Domesday and the period of the Pipe-Rolls, especially if it throws some fresh light on the vexed question of Domesday values. Moreover, we have here an obvious suggestion as to the purpose of the Conqueror in ascertaining values, at least so far as concerned the demesne lands of the Crown, for he was thus enabled to check the sheriffs, by obtaining a basis for calculating the amount of the _firma comitatus_. With this point we shall have to deal when we come to Geoffrey's connection with the shrievalty of Essex and Herts. Attention may also be called to the formula of "excambion" (as the Scottish lawyers term it) here employed, for it would seem to be earlier than any of those quoted in Madox's _Formularium_. But the suggested exchange is specially interesting in the case of Count Theobald, because it gives us an historical fact not elsewhere mentioned, namely, that the Empress, on obtaining the mastery, forfeited his lands at once. Her doing so, we should observe, is in strict accordance with the chroniclers' assertions as to her wholesale forfeitures and her special hostility to Stephen's house. And we can go further still. We can ascertain not only that Count Theobald was forfeited, as we have seen, by the Empress, but also that the land she forfeited had been given him by Stephen himself. In a document which I have previously referred to, we read that Stephen had given him the "manor" of Maldon,[336] being that manor of Crown demesne which the Empress here bestows upon Geoffrey. Another important though difficult subject upon which this charter bears is that of knight-service. Indeed, considering its early date—a quarter of a century earlier than the returns contained in the _Liber Niger_—it may, in conjunction with Stephen's charter of some six months later, be pronounced to be among our most valuable evidences for what Dr. Stubbs describes as "a subject on which the greatest obscurity prevails."[337]