In an article published in a recent number of this journal, Dr. Henry Woodward discusses the origin of the curious cylindrical cavities which occur in such profusion in certain concretionary blocks of sandstone and on exposed rock-surfaces at two distinct levels in one or two localities in the Fayûm depression. These perforated rocks, first noted by Schweinfurth, were examined by me some ten years ago and referred to as “apparently the work of marine boring mollusca” in my memoir on the region in question. Both Dr. Schweinfurth and I had considerable misgivings in regarding the cavities in question as shellborings, but in my case, and I believe in his also, this explanation appeared to involve fewer difficulties than any other which suggested itself.