the results of this friction since Neolithic times. In the Palæolithic implements, however, the gloss which so frequently accompanies a structural alteration in the surface of the flint, seems due to the same chemical cause which has produced the alteration in the structure; and this cause, as I have already remarked, appears to be the infiltration of water partially dissolving the body of the flint.
An interesting paper by M. E. d'Acy,[1] on the patination of the worked flints of St. Acheul, was communicated to the Anthropological Congress at Paris in 1878.
The dendritic markings are more common on the implements from some localities, as, for instance, Santon Downham, than from others, and are due to the crystallization of peroxide of manganese upon their surface. Although these moss-like forms do not of necessity take any great length of time for their production, as is proved by their occasional occurrence in paper of recent manufacture, in which particles of manganese have been accidentally present, yet to superinduce them on a forged flint would pass the ordinary fabricator's skill, and their presence may safely be regarded as an indication of an old surface. The same may be said of the calcareous incrustations, which also are by no means of universal occurrence. The safest and indeed the most common indication of an implement being really genuine is the alteration in the structure of the flint which has taken place over the greater part, if not the whole, of its surface, and the discoloration it has undergone. In ochreous beds of gravel the specimens are frequently much stained of a yellow, buff, or brown colour; where less iron is present they become grey, especially at the angles, and often more so on one face than the other. In red or brown marl, and in places where they lie at no great depth from the surface^ or where there is a free passage for water charged with carbonic acid, they frequently become white; whereas, in more impervious clay, they are often stained brown, or even remain black, though the surface is rendered glossy. In beds where much chalk is present they seem to have a tendency to retain their original colour. The discoloration of the surface is not always attended by the glossy appearance already mentioned, but this depends in a great measure on the character of the flint originally employed.
It sometimes happens that the upper side of an implement has been whitened during its sojourn in the earth, while its lower side has remained almost unaltered.
- ↑ C. R. du Cong. Intern. des Sci. Anthrop., 1880, p. 234.
