366 Proceedings of the British Association for 1850. 



Tessellated Pavements discovered at Cirencester (the Roman 

 Corinium)," by Professor Buckman. — In this paper it was 

 shown that the materials of which pavements are composed 

 are of two kinds : — The first derived from rocks of the dis- 

 trict and termed natural, the second composed of clay, fictilia 

 and glass, artificial tessellge. The natural tessellae, many of 

 which are so altered by chemical manipulation as to cause 

 them to be referred to foreign rocks, consist of bits of 

 stone from the chalk, oolite, lias, and red sandstone forma- 

 tions, and were clearly referred to their origin, and the pro- 

 cesses by which they were prepared for pavements were 

 pointed out. Thus a grey colour was produced from a cream 

 coloured oolite, the change of colour being caused by a pro- 

 cess of roasting. This is dependent upon the fact that the 

 oolite bed of which they are made contains iron and organic 

 matter, the latter of which prevented the iron peroxidizing, 

 and thus the grey was due to a protoxide of that metal. The 

 artificial tessellse from pottery consist of shades of red and 

 black ; the reds all being due to a peroxidation of the iron 

 in the clays from which they were made, — whilst the blacks 

 were the result of baking in " smother furnaces," as long 

 since pointed out by Mr Artis, so that the carbonaceous 

 matter of the fuel with which the baking was effected was 

 prevented from escaping, and, as he would lead us to infer, 

 the black smoke penetrated the clay and thus blackened it. 

 The author, however, showed that this smoke acted chemi- 

 cally, by preventing the oxidation of the iron, and thus the 

 change from the dark colour of the clay to red which usually 

 occurs in burning pottery and bricks was prevented. Refer- 

 ence was then made to a medallion in the pavement repre- 

 senting Flora, in the first drawing of which the head-dress 

 and flowers held in the hand were coloured verdigris green, 

 the hue these objects presented on being exhumed ; but as 

 this was unsatisfactory in chromatic arrangement, the author 

 suspected some chemical change had occurred since the 

 pavement was put down, — and on scraping away the 

 green from the surfaces of the tessellse in question, a 

 beautiful ruby glass presented itself. New drawings (which 

 were also exhibited) were then made with ruby instead 



