Post by metalsmith on Jun 12, 2017 17:15:26 GMT -5
Here's a piece of chlorite facies metamorphosed lithic greywacke slate and Quartz from Ingleton.
The greywackes are turbidites that formed from submarine avalanches along the north-west margin of a land-mass. In this case, one that existed in the geologic past, known as the Eastern Avalonia continental shelf, bordering the Iapetus Ocean (source).Originally these were identified as coming from the Precambrian (giving their name to the Pre-Cambrian age the Ingletonian) but were then thought to be Ordovician, from the Arenig. The pendulum of opinion swung back to Precambrian and in 2008, back to early Ordovician.
This to-ing and fro-ing might relate to the possibility that Pre-Cambrian and Ordovician are interleaved. The British Geological Survey is of the opinion that on balance the rocks should be considered neo-Proterozoic.
Phew! Glad that's sorted out (for now )
The following rock is from the area known as the Yorkshire Dales, a national park, home to the amazing Thornton Force...
Author: Val Vannett
The slates are shown as the lower series in this Ordovician - Carboniferous unconformity resulting in the spectacular waterfall.
Their age is now thought to be Arenig, however the previous estimation of the age of the rocks provided a sub-division of the Pre-Cambrian known as Ingletonian. It is slightly ironic that the early Proterozoic rocks from Ingleton have now been shifted out of the Ingletonian epoch. hmmm.
Of course collecting in the national park would not be considered good form.
Luckily the planners have permitted a significant roadstone quarry to be located just outside of the national park:
This is home to some green-grey continental shelf turbidites - greywacke that have been metamorphosed to green-schist facies slate then occasionally vein-injected with quartz. The quarry has only a few years of life left in it and I don't know of any other polished cabs from this location (but then who polishes Greywacke)?
Author: Clem Rutter
A particularly good description of the local geological features can be found here.
Back to lapidary and the evolution of a piece of rough through to polished cabochon:
Greywacke slate and quartz
The greywackes are turbidites that formed from submarine avalanches along the north-west margin of a land-mass. In this case, one that existed in the geologic past, known as the Eastern Avalonia continental shelf, bordering the Iapetus Ocean (source).Originally these were identified as coming from the Precambrian (giving their name to the Pre-Cambrian age the Ingletonian) but were then thought to be Ordovician, from the Arenig. The pendulum of opinion swung back to Precambrian and in 2008, back to early Ordovician.
This to-ing and fro-ing might relate to the possibility that Pre-Cambrian and Ordovician are interleaved. The British Geological Survey is of the opinion that on balance the rocks should be considered neo-Proterozoic.
Phew! Glad that's sorted out (for now )
The following rock is from the area known as the Yorkshire Dales, a national park, home to the amazing Thornton Force...
Author: Val Vannett
The slates are shown as the lower series in this Ordovician - Carboniferous unconformity resulting in the spectacular waterfall.
Their age is now thought to be Arenig, however the previous estimation of the age of the rocks provided a sub-division of the Pre-Cambrian known as Ingletonian. It is slightly ironic that the early Proterozoic rocks from Ingleton have now been shifted out of the Ingletonian epoch. hmmm.
Of course collecting in the national park would not be considered good form.
Luckily the planners have permitted a significant roadstone quarry to be located just outside of the national park:
This is home to some green-grey continental shelf turbidites - greywacke that have been metamorphosed to green-schist facies slate then occasionally vein-injected with quartz. The quarry has only a few years of life left in it and I don't know of any other polished cabs from this location (but then who polishes Greywacke)?
Author: Clem Rutter
A particularly good description of the local geological features can be found here.
Back to lapidary and the evolution of a piece of rough through to polished cabochon:
Greywacke slate and quartz