The _Inquisitio Comitatus Cantabrigiensis_ (hereafter styled 'the I.C.C.') deals with the county of Cambridge alone, but, in that county, with the lands of all holders. The _Inquisitio Eliensis_ (which I propose to style 'the I.E.') deals with several counties, but, in these counties, with the lands of the abbey alone. The latter was duly printed, with Domesday Book, by the Record Commission; the former remained in manuscript till printed by Mr Hamilton. Mr Hamilton describes his record at the outset as 'the Original Return made by the _Juratores_ of the county of Cambridge in obedience to the Conqueror's mandate, from which the Exchequer Domesday for that county was afterwards compiled by the King's secretaries', and as 'the original source from which the Exchequer Domesday for that county was derived'. Mr Birch here again repeats the words, insisting 'that we have in this very precious Cottonian MS. _the original source_ from which the Exchequer Domesday of Cambridgeshire was compiled'.[8] Such a description is most unfortunate being not only inaccurate but misleading. All that we are entitled to predicate of the document is that it is _apparently a copy_ of the original returns from which Domesday Book was compiled. For 'the original source' of both we must look to the now missing returns of the jurors, the primary authority from which Domesday Book and the _Inquisitio Com. Cant._ are independently derived. This distinction is all-important, reducing, as it does, the _Inquisitio_ from the rank of an 'original' to that of a secondary authority on the same level with Domesday Book.[9] Mr Hamilton, like Mr Webb before him, assigned the handwriting of the _Inquisitio_ to about the close of the twelfth century. The copy of the returns which it contains, therefore, was made about a century later than the returns themselves. The problem then that we have to solve is this: 'Is the I.C.C. an actual transcript of these original returns, and if so, is it faithful?' I will not, like Mr Hamilton, assume an affirmative, but will attempt an impartial inquiry. The two paths which we must follow in turn to arrive at a just conclusion are (1) the construction of the I.C.C., (2) collation with the _Inq. Eliensis_. For I hope to show that the latter record must have been derived from the same source as the _Inq. Com. Cant._