The evidence of the Stone Implements goes far to give the date of the building. Horn picks similar to those employed at Stonehenge have been found in considerable numbers at Grimes Graves, where they were used for excavating chalk in order to win flint for implement making. Other picks have been found at Cissbury, near Worthing, where similar chalk workings existed. This resemblance between the finds at Stonehenge, Cissbury, and Grimes Graves, does not, however, end with the picks; it is repeated in the similarity of the Implements of Stone, those at Stonehenge being in some cases the counterpart of those found in the other localities. The Cissbury Implements have been assigned "to the Stone Age, or at any rate to the Age of Flint manufacture" by General Pitt Rivers, who discovered and reported upon them. Canon Greenwell describes the Implements from Grimes Graves as belonging to "a period when both metal and stone were in use." It is obvious, therefore, that the similarity between the tools used in the construction of Stonehenge, and those used in other parts of England for similar purposes, and definitely assigned to their period in the history of Man, demonstrates very clearly that the date of the building of Stonehenge may fairly be placed at a time when the use of stone was continuous with a partial use of bronze; and that if Stonehenge is not a Neolithic structure, it must certainly belong to the Early Bronze period. It might be urged that the roughness of the Tools, coupled with the marked absence of bronze, indicates an even earlier period than that already stated, but it must be remembered that the form of the implement is not always a criterion of its age. Moreover, bronze tools were not necessary for the dressing of the Stones, though had they been plentiful, it is more than probable that some might have been either lost or dropped during the work, and would have come to light during the excavations. Yet another sidelight upon the date of Stonehenge is to be found in the presence of chippings of foreign stone found inside some of the neighbouring Bronze Age barrows, which prove conclusively that the barrows must have been built at a date later than the erection of Stonehenge.