The preparation and utility of laminar collodion moulds for recording relief features in natural surfaces of fossil plants is well known from the writings of Professor A. G. Nathorst (1). Equally familiar is the technique of Professor J. Walton (2) for making cellulose acetate “peels” from ground and etched surfaces of rocks containing carbonized remains of vegetable tissues. More recently, similar methods have been adopted by Dr. S. Leclercq (3) for studying fossil corals, by Professor A. E. Trueman (4) for examining ammonites, and by Dr. J. K. S. St. Joseph (5) and Dr. J. Weir for the analysis of fossil brachiopods. In these several cases, ground and etched specimens were prepared, from which cellulose nitrate or cellulose acetate moulds were taken. Hitherto, however, no corresponding technique appears to have been used either for research upon inorganic rock-structures or for the investigation of surface relief-characters of minerals.