Strinds and Dolyhir Quarries Sunday 24th October 26, 1999
The field trip was lead by Jill Smethurst and on a very wet Sunday morning about 20 of us assembled at Strinds quarry. This is a working quarry and Jill first pointed out various lagoons used to filter out the sediments before the water flows into the local streams.
The Strinds formation is of Silurian age and this overlays the Precambrian beds, the limestone Silurian beds dip at about 60 to 70. The limestone overlay the Precambrian beds unconformably and between these beds is a conglomerate bed. The Cambrian and Ordovician are missing and have either been eroded or were not been deposited.
Various boulders along the roadways showed the different type of conglomerate deposited and this varied form dolerite and basalt stones with small quartz stones. These probably come from the Hanter Staner complex we visited on Staurday. Other boulders contained large well rounded quartz crystals, quite different from the granitic rocks of the Hanter Staner complex. These quartz crystals have been transported a larger distance and may have come from Snowdonia area.
The quarry is on the edge of the Welsh Basin and before deposition of the conglomerate the level may have arisen as a Hoist and this would have lead to no deposition during the Cambrian and Ordovician times.
Faults were quite noticeable and a hoist was seen in the Precambrian.
At a higher level in the quarry were limestone boulders and some of these were very some fossiliferous beds. These contained corals and bryozans. The following fossils were found:-
Corals Heliolites interstinctus Wenlock series
Labechia confera Wenlock series
Brachiopods Eospirifer radiatus Wenlock series
Meristina obtusa Wenlock series
Bryozans Favositella interpuncta Wenlock series
After a very wet morning we adjourned to a very pleasant local pub for lunch.
In the afternoon we visited the adjacent Dolyhir quarry, this quarry is mainly use to deposit spoils. We were stopped at the entrance to the quarry and asked to look at some Silurian limestone deposits, with muddy bands. These limestones contained many larger well rounded stones which were deposited across bedding. A fairly complete coral and quite a large layer stromatalite were found.
In the quarry proper the Strinds beds here look quite different to those in the Strinds quarry. There has been quite a lot of hydro thermal activity and this has lead to alteration of the Strinds formation. This was very noticeable in a band about 2 to 3m wide at an angle of about 450, and this was red due to hematite. Whether or not the angle was due to bedding was not clear. John Jaggard, our leader on Saturday was hoping to show us a dolerite dyke, but at first it looked to have been quarried out. The dyke could still be seen further back and was about 15m wide, this appears to have formed lower down and been emplaced as a solid as there is no sign of any chilled magins. The dolerite dyke contained some chaloporite.
Further up the quarry we were shown a turbidite formation, this was seen to be overturned as the sole marks were upper most on the coarser grained material, this graded out to a shale and cross bedding and planar bedding was shown. This sequence was repeated two or three times.
We suffered a further disappointment when some mineral veins Jill was hoping to show us had been covered by spoil. But we did manage to find some looses rocks with blue/green malachite and bright blue azurite crystals.
One advantage of the wet weather was to make the fossils seen during morning and crystals in the afternoon stand out.
Our thanks to Jill Smethurst for leading a very informative visit to the quarries and to John for his assistance and last but not least to Shelia for organising our Weekend trip.