The distribution of the water-bearing strata in the city of Edinburgh is a question of considerable economic importance. It has had an important bearing on the development of the local brewing industry. A careful examination of the sites of the various wells shows the intimate relation between the geological structure of the district and the available sources of supply. Many of the wells are situated in localities where a copious discharge of water might naturally be expected in view of the lithological characters of the strata and their geological relations. In connection with this inquiry confidential information regarding journals of bores, the depths of various wells, and the nature of strata passed through in sinking the wells has been kindly supplied by various companies. Important evidence has thus been obtained for which I tender most cordial thanks. In some cases permission has been given to examine the cores of bores and the materials pierced in the wells. These investigations have led to the identification of some fossiliferous bands and the determination of the division of the Carboniferous system to which they belong. This detailed information is now deposited in the archives of the Geological Survey of Scotland, and cannot be published without the consent of the parties who gave it. In a general way it may be stated that it confirms most of the main conclusions concerning the distribution and the relations of the rocks as set forth in the Geological Survey memoir on “The Geology of the Neighbourhood of