We are very grateful to F.W. Smith for his thoughtful consideration of the brief speculation we included in our paper about the origins of the permeable features encountered at 411 m depth in what is now known as the Eastgate No. 1 Borehole (Younger & Manning 2010). His remarks are very enlightening, and add significantly to the published record on the structural geology of the North Pennine Orefield. Dr Smith's comments actually penetrate a point of amicable difference between the two of us, with Younger being in favour of a predominantly structural interpretation, whereas Manning was more inclined to an explanation that also involved deep weathering.

As it happens, further work undertaken at the site in 2010 has since shed further light on the matter, and would tend to support Dr Smith's suggestion that the empty voids found at 411 m depth in Eastgate No. 1 are essentially …