Many workers in the domain of the petrology of sedimentary rocks will welcome the article by Dr. Rastall in the Geological Magazine for January, 1923, and will appreciate the fact that certain notes therein help to make clear what may or may not reasonably be expected from this branch of geology. Judging from what has been said and written from time to time, I fear there is some amount of misconception as to what is being and has been achieved by the study of the rarer minerals and grain-size of sediments. As Dr. Rastall has paid me the compliment of referring to certain work with which I was concerned, in part during the war, it may be of interest and service if I indicate briefly the character of some of the work done and the utility of the petrographic methods adopted.