The Sugar Loaf is one of the main three mountains around the market town of Abergavenny - the other two being Blorenge to the south and The Skirrid to the north-east. Reaching the height of 596 metres above sea level at the headline co-ordinates (the trig point) it certainly is not the highest mountain in South Wales but it has a huge popularity due to it's proximity to Abergavenny and it's ease of access. Also, as you drive in from the east on the A40 dual carriageway it cuts a fine outline against the sky showing off it's volcano-esque or sugarloaf-esque profile which gives it it's name. But why is it even there? This is the subject of this earthcache.
The Geology
The geology of Monmouthshire consists mainly of thick layers of sedimentary rock, and the Sugar Loaf is no exception being made mainly of Old Red Sandstone from the Devonian period (about 416 to 360 million years ago), in common with the rest of the Black Mountains. Old Red Sandstone is a group of rocks that were deposited in varying environments and include mudstones, siltstones and various conglomerates.
Old red sandstone is continental (rather than marine) in origin when thick layers of sand and mud were deposited, probably in basins and compressed over time to eventually form rock. Often animal, plant and fish remains are present (but not always) as was oxidised iron minerals that give its distinctive red colour, but again not always as colour can vary. The texture is normally gritty in nature.
The Old Red Sandstone that forms the Sugar Loaf overlays Red Marl - a type of mudstone, but, more importantly for this earthcache, at the summit (right on top of the Old Red Sandstone) was a thin layer of a Quartz Conglomerate, which was a very hard rock, this Quartz Conglomerate is in line with the layer on Blorenge (see diagram below):
Conglomerates are still sedimentary rocks but they contain course-grained fragments of size 2mm and larger, known as clasts. Essentially these fragments are from pre-existing rock that has been weathered, eroded or broken apart previously, and they then get picked up and mixed up in the formation of the new rock. During the formation process what essentially happens is that sediment is compressed, any fluid that is caught in pores is expelled and rock is slowly formed - a process called lithification. The clasts get trapped and caught up in this process and the result is a conglomerate.
Thus a Quartz Conglomerate is a lithified sedimentary rock that is primarily composed of rounded pebbles of quartz - quartz being an crystalline igneous (volcanic) rock. The look is often cement-like and the texture similar but will vary depending on the size of the quartz composition. It is a very hard rock due to the inclusion of the quartz fragments.
The Usk valley (which is to the south of Sugar Loaf with the Usk river in) and the Grwyne Fawr valley to the north were formed by a glacier in the last ice age. As the glacier flowed from the west, from where the Usk reservoir is today it travelled down from Brecon to Crickhowell and divided to the north and south at Crickhowell to eventually create the current valleys which LLanbedr and Abergavenny now occupy, leaving the robust rock we now call Sugar Loaf. Also the Quartz Conglomerate at the summit acted as a cap, because it is so hard, kept Sugar Loaf's height due to it resisting the effects of weathering and other erosion.
Visiting
The first parking co-ordinates take you to the main car park on the 'front' of the mountain. This is the south side and overlooks the Usk valley and is approached from Pentre Lane on the Brecon road from Abergavenny. I have also added a second car park which approaches from Forest Coal Pit to the north. This route is much, much quieter and is just as dramatic in it's approach but you will need to do down the south side of the mountain a little way to reach stage 1.
Either way the Sugar Loaf can be considered a 'proper' mountain and you will need to be attired and prepared accordingly and with good, grippy footwear. The walk up from either way is on public footpaths marked on Ordnance Survey maps. There are also numerous other routes to the top and which one you choose is of course up to you.
The Tasks
To log this earthcache you will need to visit the different stages, in no particular order, and send the answers to me to the questions below:
1) Head up to stage/waypoint 1 and take a look at the rocky outcrop. Describe the rock (think of composition, texture, colour etc) and tell me what type of rock it is. (Don't make assumptions though - you will need to actually look at the rock properly and read the information above as very few people have got this correct).
2) Go to stage/waypoint 2 and take a look at all the rock around you. Again describe it and decide what type of rock this is.
3) Look particularly at the slanting rocks at stage/waypoint 2. What physical characteristic suggests to you that these are a type of sedimentary rock?
4) I mentioned the fact that the Usk valley was formed by glacial erosion but from the cache site at the trig point tell me what you can see that confirms this? (A bit of extra research may be needed).
You do not need to wait until I reply to log your find, but I will come back to you to either confirm or clarify your answers as soon as I can. Photos at the trig or the view are always appreciated of course but are not a condition of logging.
Many thanks to the National Trust, for allowing me to place this earthcache here.