Thin sections of clays are not easily prepared by the routine petrographic methods. The chief difficulties are due to the extremely fine texture of the clays and to the soft and plastic nature of these materials. These difficulties are only too well known, and, although in some cases they have been partially overcome by impregnation in vacuo, it is safe to assume that really little work has been accomplished in the microscopic examination of clays on account of the difficulty of producing satisfactory thin sections. The writer has attempted to extend the scope of the microscopic investigation of clay rocLs by means of the technique outlined below.

The method has been devised in response to an appeal by a friend, who, working in a laboratory at a well-known pottery works and thus connected with the clay industry, desired a method that would make possible the examination of thin sections of clays under high powers with polarized light.