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SURVEX - colour by geology?

Duncan Price

Active member
A geologist caving friend is mapping the geology of Wookey Hole. Contrary to the reports of cave divers, Chamber 24 is virtually all formed in conglomerate. He's put together a map in some geological software that shows it but asked me yesterday if it was possible to get SURVEX to colour code the points - I know that you can colour code for depth (default), error etc. but wondered if anyone has a fix to generate colouring for rock type? Wookey Hole is formed in dolomitic conglomerate and limestone with exposure of tea green marl in the roof of Land of Hope & Glory. Nick has drafted a map based on geology, I've attached grabs of the survey coded for date and style (the data is mostly normal caving survey with some diving bits and the section from 24 to 25 is cartesian from digitizing John Cordingley's diving survey). I suppose I could frig the data by using spurious date settings to generate the four colours required (to include "not mapped") but this seems a bit of a pain as it would require going through all the surveys and manually editing them. Ideas welcome.


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You definitely can in therion (Least helpful answer ever!), and the quick way to do it would be split the survey into 4 segments and then join them - that should give you the required .svx output needed too but it's not really much different to what you've suggested and may well be slower if you've not used therion.

It's been a while since I played around with things just on survex... can you batch edit them by exporting the .csv to excel (or equivalent) and then recompiling in survex?


Well-known member
Playing with the dates is definitely the easiest way within the current version of survex & I guess it's not really an issue for many cavers, as we are usually working within one rock type (in Yorkshire & South Wales the strata are pretty much aligned with depth data anyway). So, if someone is creating a fix it will ideally allow identification of different beds of rock & somehow show the relative depths as well?


Active member
A possibly more versatile solution for a geologist in this case is to use a traditional GIS package to update and analyse the data. This can be done in QGIS using Patrick Warren's QGIS 3D file importer, which I use very regularly. It creates a geopackage layer with an attribute table derived from the survex file, all with the click of a button (very simple GUI). You can then add a geology field to this, and also do other GIS analysis using additional data such as geological maps or terrain data very easily. You can even make 3D visual analysis in QGIS 3 these days - although it's not as good as survex its still fine for most static visualisations.


Well-known member
Sounds a really interesting project! The detail has gone over my head already but I know my geology OK, so I'll be watching this one.

Andy Farrant

Active member
It would be great to see a 3D model of the geology of Wookey Hole, as the geological structure and the unconformity has a big influence on cave development. Passages tend to be quasi-horizontal with vertical rifts in the conglomerate, but more classic looping passages in the limestones. The geological structure of the Carboniferous limestones will be interesting to see, as I suspect the deep sump at the end (Wookey 25) may be rising up dip on the northerly dipping limb of an anticline, so worth recording dip and strike values if possible. The large 'neptunian dyke' (fissure fill) infilled with younger Triassic marls (Blue Anchor Fm) impregnated with celestite in the roof of Land of Hope & Glory is one of the best examples on Mendip. There is a really interesting structural story to decipher from this and the calcite veins in the blasted tunnels between Chamber 9 and the exit, and in the new tunnel leading to 20 which has a fine section through the unconformity. Wookey 20 is a really deep phreatic loop and it looks like the water probably rose back up via Wookey 22 ('upstream') and out via Halloween Rift? All in all, it is one of the most geologically fascinating caves in the UK.

Other than the suggestions above, exporting the data into a GIS package may be the best bet, or simply adding in the geology in a drawing package? There is a variety of 3D geological modelling software available, some for free (eg https://www.bgs.ac.uk/technologies/software/groundhog/) which can use GIS shape files or CAD drawing data to import data and create models.

I hope Nick has plans to write this up (happy to help).



Well-known member
Andy; you wrote: " I suspect the deep sump at the end (Wookey 25) may be rising up dip ".

I reckon you're right. In the terminal sump, from -60 m up to about -8 m (below the final ascent to airspace in Chamber 25) is all up dip, along (probably) a single bedding plane. The passage trend isn't at 90 degrees to the strike though, as the passage floor slopes from right to left when heading in - that may be useful to bear in mind if you're trying to elucidate the true directions of dip and strike.

From around -60 m the route of the diver swings right (going into the sump) so the deeper upstream continuation from here trends closer to the strike than to the dip.

The descent from Chamber 25 en route downstream to surface in 24 is very steep and a bit bouldery. It may be that a small fault outcrops in the Chamber 25 area and guides the steep first part of the sump downstream from here to Wookey 24.

I'm far from expert on Wookey Hole but the above observations may help.

Duncan Price

Active member
I'm far from expert on Wookey Hole but the above observations may help.

I digitized John's survey of the final sump and having been as far as just beyond Parker's 1985 limit agree with him. When my tape measures are out of the static sump between 22 and 23 we'll move them to the 24-25 sump and resurvey it using the underwater DistoX and SONAR wand. The aim is to get an accurate survey as far as we can upstream. The inclined bedding beyond The Well (upstream of Chamber 25) is like the strike passage in 22 which is also seen in Wookey 23 3/4 and Fool's Gold in 24. This feature has been pushed to -3 m and there may be airspace up the (probably another feature like 23 3/4 God help us!) [CDG NL 124:34 (1997)]