It has not hitherto been clearly made out in what way these Carboniferous patches are related to each other. Some have considered it doubtful whether the three former are in any way represented in the Coalbrook-dale Field. The prevailing impression is, I believe, that the Clee Hill Fields are quite distinct in point of age from any of the Coal tracts surrounding them, and were formed in a depression sufficiently low to receive the Millstone Grit which we find to be wanting in the extensive Coal-fields to the East and North-east, except, let me observe, along the Western margin of the Coalbrook-dale district, where it is not well developed, but still represented. Eastward of that margin, however, it thins out rapidly, and gives way to the Silurian flooring of that Coal-field.