The East Twll represents a second working from the surface, begun in the late 1850s or early 1860s. It extended down to Level 34, with an adit at Level 2, but seems to have been abandoned with the driving of Level 9 by 1871, which allowed the development of underground chambers. In this state the East Twll is shown on the 1st edition of the 25-inch O. S. map, 1889, the Level 2 adit disused. Its present form is the result of the collapse of underground chambers in 1900, causing massive surface subsidence.
W J Crompton, RCAHMW, 22 April 2009.