This system seemed so reasonable and philosophical, compared with the wild theories of the British antiquaries of the last century, that it was instantly adopted both in the country of its birth and in England and France; and the succession of the three ages--stone, bronze, and iron--was generally looked upon as firmly established as any fact in chronology. Gradually, however, it has been perceived that the hard and fast line at first drawn between them cannot be maintained. At the last meeting of the International Archæological Congress, held at Copenhagen in the autumn of 1869, it was admitted on all hands that there was a considerable overlap between each of the three ages. Men did not immediately cease to use stone implements when bronze was introduced; and bronze continued to be employed for many purposes after the use of iron was well known.[15] Antiquaries have not yet made up their minds to what extent the overlap took place; but on its determination depends the whole value of the scheme as a chronometric scale. If the Danes, instead of breaking up their "finds" and distributing them in cases according to a pre-conceived system, had kept and published a careful record of the places where the contents of their museums were found, and in what juxtaposition, we should not probably be in our present difficulty. Under the circumstances, it is perhaps fortunate that we had no central museum, but that our antiquaries have published careful narratives of their proceedings. Sir Richard Colt Hoare's great works are models of their class, but are scarcely to be depended upon in the present instance, as the importance of flint and flint implements was not appreciated in his time to the extent it now is.[16] The explorations of the Messrs. Bateman in Derbyshire are more completely up to the mark of the science of the present day. A few extracts from one of their works will show how various and how mixed the contents of even a single group of tombs are, and will prove consequently how little dependence can be placed on any one class of objects to fix the age of these monuments. In his 'Vestiges of the Antiquities of Derbyshire,' published in 1848 by Thomas Bateman, we find the following among other interesting facts, taking them as they are found arranged in his volume, without any attempt at classification:-- On Winster Moor (p. 20), a gold Greek cross--undoubtedly Christian, with a fibula of the same metal richly ornamented, and a quantity of glass and metal ornaments. Pegges Barrow (p. 24). Several Anglo-Saxon ornaments, most probably of the seventh or eighth century. In a barrow at Long Roods (p. 28) were found two urns, with calcined bones and a brass coin of Constantine, of the type "Gloria exercitus." In Haddon Field Barrow (p. 30) were found 82 brass coins: among them Constantine 9, Constans 17, Constantius II. 9, family of Constantine 3, Urbs Roma 1, Constantinopolis 2, Valentinian 5, Valens 12, Gratian 3. The remainder illegible.