To the west of Wimberry Colliery, the Coleford High Delf seam outcrops from two prominent inliers located on the crest of the anticline axis known locally as “The Ridge.” These outcrops, in both Wimberry and Howlers Slades, are dotted with numerous old adits. The most significant is Thatch Water Level in Wimberry Slade, which trends NNW for approximately two-thirds of a mile, following the strike of The Ridge. In Wimberry Slade, the Yorkey seam was exposed, varying in thickness from just 9 inches to as much as 3 feet 4 inches. It was also worked in Howlers Slade from No. 1 and No. 2 Newroad Coal Levels.

Also Wimberry Slade North Free Mine - 2 adits at SO 6030 1230

• 1875 Mansfield & Osborne
• 1880 J.T. Thomas
• 1885 T. Thomas & Co.
• 1890 Buckholt Colliery Co.

The main shaft struck the Coleford High Delf seam at 129 feet and exploited its steep dip via crosscuts at 99 and 249 feet—the seam’s highest and lowest worked levels. The upper level was connected to the surface through Mushet’s Old Furnace Level in Howlers Slade. Extensive workings also developed in nearby slades, including Wimberry and Howlers, where various outcrops and levels were driven during the 19th century. In the 1890s, the mine experienced a severe inundation, which temporarily halted operations; however, it was later reopened.

This complex of workings lies near the axis of “The Ridge,” between Wimberry and Howlers Slades, west of Wimberry Colliery. Mushet’s Old Furnace Level, the Thatch Water Level, and the various Newroad Coal Levels can still be traced through overgrown paths and old adit mouths, although most entrances are now collapsed or obscured.