From the introduction: The extensive and ever growing literature which contains the results of investigators who have made use of the method of etching in order to obtain a more exact knowledge of various phases of crystal symmetry, is an evidence of the importance of this series of phenomena as a means of crystallographic research. Among these publications there have appeared from time to time papers which have been devoted to the study of etch-figures themselves rather than to their secondary application. It is evident from a study of these articles that many of the processes involved in the origin and growth of etch-figures have not yet been fully explained, and as these processes are intimately connected with the molecular structure of crystalline matter, the value of fuller information will readily be conceded.