AND REMARKS ON THETR CHROMATIC ARRANGEMENT. 349

to the following list, under the heading — Natural and Arti- ficial Tessellse. Natural TesseUa 1 . White . . . . Formed of Chalk. 2. Cream-colour . . . Hard, fine-grained Freestone, from the great Oolite. 3. Grey ... , . The same, altered hy heat. 4. Yellow .... Oolite ; Oolitic and Wiltshire pebhlos. 5. Chocolate . . . . Old Red Sandstone. 6. Slate-colour, or black . Limestone bands of the Lower Lias. Artificial Tessellce. 1. Light red ^ 8. Dark red [■ . . . Formed of Terra Cottn. 9. Black ) 10. Transparent ruby . . Glass. 1. The Natural TessdlcB. The tessellce, by this list, will be seen to be derived mostly from the immediate district. The cream-coloured stones form the groundwork, sur- rounding the designs, and filling in some of the cords of the borders. This material is a fine-grained oolitic freestone, found in the Great Oolite formation, around Cirencester, in which it occurs as a bed, about four feet in thickness. It is of a light tint, and does not change colour on exposure. Its appearance in the quarry is so like the other beds of this rock as to have been overlooked ; and hence it has been supposed by Lysons, and other authorities, that this parti- cular stone is of foreign origin, and it has by them been named " Polombino marble," which indeed it much resembles. Some pieces of this oolitic stone were found mixed with the rubbish in Dyer Street, at Cirencester, and which there is reason to believe had been brought from a neighbouring quarry to make tessellse of ; we may therefore suppose that the different sized fragments were chipped off as a supply was required. The grey, marked 3, was the most difiicult to refer to any known rock, both from its colour and texture. The latter, however, on close inspection, appeared to be exactly that of the cream-colour, wliich the microscope proved to be the case.. The question as to the difference in tint became one of interest, and upon being made a matter of experiment, it