Geology of Blue John Cavern
Castleton and District is of great interest to geologists. The Blue John Cavern and the area immediately surrounding it are of immense educational interest. Showing clearly how the caverns were formed in the Limestone strata by the action of water from the melting ice of the glacial periods (the last of these estimated at 80,000 year ago), and also how the Limestone itself had earlier been laid down as a deposit on the sea bed millions of years ago.
Perhaps a series of small diagrams can illustrate here what is believed to have happened.
(a) Shows the strata of
- Carboniferous Limestone 250,000,000 years ago.
- Yoredale Shale and milestone grit.
(b) Shows the same strata at a much later period when "buckling" occurred either simply due to the contraction of the earth surface on cooling or more likely due to direct volcanic action. (Evidence for this can be found locally) A "fault" also can be seen.
(c) A mere 80,000 years ago, when the ice of the last glacial period was melting. The water. Having enlarged a series of vertical and horizontal cracks. Flowed as an underground river and then at a much lower level to join other similar torrents and "scoured out" the Hope Valley.
(d) The Present day scene - the underground torrent has ceased to flow, leaving behind this range of caverns: and in the intervening period of time since the last "Ice Age" denudation (the action of the elements - wind, rain, frost, and sunshine) has so worn down the surrounding hilltops and silted debris down into the valley below as to completely cover the huge natural exit from the cavern which must have existed while the ice was melting and the resulting underground river was able to flow. Mam Tor (The Shivering Mountain) the Odin Fault and the Winnats pass are now Identifiable.