In the Geological Magazine for April, 1871, I attempted to account for the mode of occurrence of the masses of Carboniferous Limestone that are found in the midst of the Coal-measure country at Luckington and Vobster in Somersetshire, and I then drew a picture of a faulted and inverted anticlinal to explain the phenomena. Mr. McMurtrie, who has more recently re-opened the discussion on the subject, and in a friendly manner assailed my theory, again asserts that the Limestone masses “must in some way have been folded over” from the Mendip range. He has very clearly brought forward all the local facts that bear upon the question, and has represented in diagram the mode by which he would account for the position of these isolated areas of Carboniferous Limestone. No one is so familiar as is Mr. McMurtrie with the detailed structure of the Somersetshire Coal-field, and I look forward with great interest to the facts which he is enabled from time to time to bring forward; nevertheless I may be pardoned for still differing from his general conclusions, inasmuch as the facts at present made known appear to me neither to upset my own theory, nor to establish that advocated by Mr. McMurtrie. Indeed it is only due to him to observe that he does not consider the question as finally settled, although he brings forward facts which seem to him to militate against the theory I ventured to propose.