It is well known that, though the Coal Fields of Lancashire and North Wales are now parted from one another at the surface by a broad tract of New Red Sandstone, there is reason to believe that the two are connected underground, and are bothparts of one and the same great deposit; and that the beds which in Lancashire and Cheshire dip out of sight below the Redmeasures, reappear in Flintshire and Denbighshire. Attempts have been made, I believe, to identify the individual coal-beds of the two districts, but I do not know with what success. During a short stay at Llangollen, some years ago, I venturedon a like task for the Lower Carboniferous Rocks, and though the time at my disposal allowed of only scanty observations, these were recorded in my note-book, in hopes that an opportunity might occur of filling in the sketch thus roughly tracedout. No such chance has befallen, or seems likely to befall me, and in the hope that the notes I then made may aid some one who, with more leisure, is willing to attempt a full solution of this problem, I now put them forward as a rough approximation.