Many ingenious methods and materials have been used for the making of geological models, to show the internal structure and outcrop of a stratified sequence, to furnish maps and lines of section, and to indicate the direction and effects of faults.

Such materials and methods as those of Mr. Sopwith, while most instructive and interesting, are powerless to deal with problems of curved strata, and no material has yet been found by which satisfactory stratigraphical models can be made of folded districts. Such a material must have several properties: —

1. It must be easily made into large plastic sheets of even thickness and of distinguishable colour.

2. It must bend readily and adapt itself sweetly to any surface to which it may be applied.

3. Successive layers must adhere together fairly quickly and quite firmly.

4. The material should set into a rigid but not brittle mass in the end, and yet not be too hard, so that it can be carved readily, or if necessary moulded into any required shape.

5. It would be an advantage if it was cheap.

Casting about for such a substance I have found one which satisfies a good many of these requirements. Not only does it allow of the building up of models out of definite stratigraphical elements in exact imitation of the natural geological structure, but it may possibly be of use in solving certain obscure structural problems. It is also likely to be of considerable use to teachers and students, as models can be built up by or before a class, and it may even have some applications outside geology itself.