Location
Hobbs Quarry is located east of Longhope and north of Little London. It can be approached on foot on public footpaths from either locality. If driving, turn off the A40 onto a minor track at X. Follow the track some 300m or so uphill and you will see a gate on the left, at the start of the woods P. The Wildlife Trust say that you can park in front of the gates if you are careful not to block the lane and are just visiting the quarry. The entrance to the reserve is some 20m uphill from here via a kissing gate.
Entrance to the Reserve
Follow the path south into the woods until you come to the information board I. Unfortunately I did not find that GPS reception was very good in these woods, however the path to the information board is very clear, so you should not need your GPS once at the reserve. The steps down to the quarry can be found a little further along the path from the board.
The Geology
Hobbs Quarry is designated a Geological SSSI. It contains well preserved exposures of ballstone coral reefs. These are limestone features that formed in shallow tropical seas which covered this area some 445 Million years ago during the Silurian Wenlock Period. In the quarry face you can see two distinct types of Wenlock Limestone. The majority of the face comprises of thinly bedded and coarse grained fossil bearing limestone which is deposited and draped over large fine grained limestone reef structures or ‘bioherms’.
Bioherm / ballstone
The bioherms are mounds which have little or no sedimentary structure. They were termed ‘ballstones’ by the quarrymen due to their circular appearance. These reefs were built up by an algae called Girvanella, as well as by corals and stromatolites (or algal mats). The overlying bedded limestones contain fossils such as brachiopods, crinoids and trilobites.
Although these beds would have been deposited horizontally, the weight of overlying deposited sediments has compressed the beds around the ball reefs to give a folded appearance. This is termed ‘differential compaction’.
View of Hobbs Quarry Face
Stone from Hobbs Quarry was not regular enough to be used for building stone. However, it would originally been used in lime kilns to make lime for mortar and as fertilizer. There are examples of lime kilns in Coleman’s Wood to the south of the main face and also in Kiln Wood to north of the track by the reserve entrance.
The woods around Hobbs Quarry are a Gloucestershire Wildlife Trust Nature Reserve who purchased the site in 1981. The diverse flora and fauna include Oak, Ask, Birch, Field Maple and Great Butterfly Orchid as well as many species of tit and common dormouse.
Note on safety:-
The floor of the quarry is uneven and may be slippery at times due to leaf litter so please take care. You should not need to approach the face of the quarry to be able to appreciate the reef structures. If you intend to go near the higher, crumbly or overhanging faces, it is advisable to wear a hard hat, as there is much loose material that can fall at any time. Please use your common sense! Hobbs Quarry Nature Reserve is a SSSI (Site of Specific Scientific Interest). You MUST NOT use a hammer on any of the faces. There is usually plenty of loose stones lying on the floor of the quarry, that have freshly fallen from the face. You may look through the fallen rocks for fossils but please keep clear of the main quarry faces for your own safety.
Questions:- To claim this Earthcache please contact me using GC MESSENGER (through my profile) to give me the answers to the following three questions:-
1. Standing on the bottom step, look to the left at the impressive Ballstone/Bioherm. Estimate the height in metres of the un-bedded central part.
2. The bedding at Hobbs Quarry is very well defined. There is a lower and less ‘active’ section of quarry face immediately opposite the bottom of the stairs which can be approached with care. Look at the beds here and especially the thin layer between the beds. In what way are the thin layers different? How would this make the bedding seem more obvious?
3. There are many small pieces of rock lying on the quarry floor. Carefully look through these to find one that contains fossils. It will not take you long! Do you think that the most of the fossils in these rocks are complete? Explain what may have been happening just after these animals died to cause this state of preservation.
Although not required to claim this Earthcache, I would be interested to see your photos from the Quarry and especially any pictures of fossils you pick up from the loose blocks.
Enjoy your visit to Hobbs Quarry
o0o Congratulations Slyatslys for being the FTLog this EarthCache. o0o
o0o Congratulations Razorfishy & Geotot for being the STLog this EarthCache. o0o