The rock at Decew Falls
Because of its thickness, the elevation and the placement of shales beneath the rock I had long suspected the Decew Formation to be a likely cave forming strata. Sadly today’s trip to Decew Falls proved me wrong but all was not lost as the geology was interesting and the scenery – beautiful.
This is Jeff as we began our scramble down into the gorge; he stands upon the promionant strata in the area, a fine grained grey dolostone of the silurian age – the Decew Formation. The rock here can be found in a thickness of up to 12 feet – great for the development of nice big tunnels. The fact that the strata is underlain by the Rochester shale added to my hopes of it being “a cave bearing formation”. The shale is somewhat impervious to water so water within the rock pools above the shale and by its movement and dissolving action bores out tunnels.
The decew Formation can be seen as far west as Hamilton, the obvious conchoidal fracturing being a feature that immediatly identifys the strata. You will notice, when weathered, the rock cleaves off in saucer shaped scoops – this is conchoidal fracturing.