Local Geology

Post your topics related to useful resources and research.
Post Reply
User avatar
Phil2401
Posts: 1191
Joined: Sun Dec 04, 2016 3:31 pm
Has thanked: 684 times
Been thanked: 608 times

Local Geology

Post by Phil2401 » Fri Mar 23, 2018 11:02 pm

Forgive me if this has been posted before.

The British Geological Survey "Geology of Britain' map provides a reasonably accurate indication of local geology -

http://mapapps.bgs.ac.uk/geologyofbritain/home.html

Start on the right hand side 'go to location' tab and enter the postcode.

Then on the left hand side use the 'Geology Key' tab to see what the various colours represent.

I guess what we're most interested in is the surface layers, so also on the left hand side you can choose between 'superficial only', 'bedrock only' or both.

So what use is this? Not a great deal really, but if you have hollows or indentations in the land, depending on the soil / subsoil type in that area they could be excavated chalk pits, gravel / sand pits, etc. rather than anything more interesting.

Phil


Quaerite et invenietis

Minelab Equinox 800
Deus Lite
Deeptech Vista Warrior

Garrett carrot
Fond Hope

User avatar
Twit
Posts: 779
Joined: Thu Nov 23, 2017 7:00 pm
Has thanked: 1316 times
Been thanked: 525 times

Re: Local Geology

Post by Twit » Sat Mar 24, 2018 3:32 am

Knowing the geology is very useful in my opinion. Here are a few examples with just the topography that I know :

You can judge how any surface has likely erroded over time and estimate the boundary between the original subsurface and modern soil deposits, the depth of the boundary or where topsoil gives way to older layers on steeper slopes.

You can figure out where mining activity would have been likely.

When you look at ploughed land you can sometimes judge the depth of the topsoil by if the plough has mixed up the older layer.

Natural fields, solid subsurface, now silted lakes and their old shores, construction materials, expected pre-modern flora, coastal erosion, ancient river paths and levels can be used to help gain a picture of where you are standing in times gone by.... are you on deep fresh silt, or would people bother to build where you are, and how?

Those are just examples, and there is no guide I know of to this so you have to do your own research and use own imagination - for me this has helped much more than just using some written account of an area. Instead I look at how the land is laid out around me when I am there, with that and any other knowledge in mind, and quite quickly hone in to where there are different possibilities of making finds... most people do that anyway using info like footpaths or relating to known features in some way, but geology adds another very different layer of understanding to it all. Geology is not just the maps either, it is also being able to look at different kinds of soil and judge its age and how it was formed, same for rock - how old its surface is.... over centuries, and especially with human activity, it may be stripped of its boundary or it may be the actual boundary with only most of the topsoil lost. There are ways to tell and the only place to start is by getting to know the terrain you are actually working on as best you can.



That is not to say it is foolproof, but much more often than not, the areas I write off as not too interesting, when I do eventually search them, I find little or nothing.

poly
Posts: 49
Joined: Mon Dec 19, 2011 6:34 am
Has thanked: 28 times
Been thanked: 50 times

Re: Local Geology

Post by poly » Sat Mar 24, 2018 8:15 pm

I’ve been a professional field geologist / palaeontologist For almost 40 years and can only totally agree with all your comments twit.

I tend to read a landscape automatically, know the underlying rock types before even knowing the actual described geology just by assessing vegetation, soil structure and type, shallowness or steepness of slopes, overall terrain, field stones, presence or absence of running water, existence of springs etc.. Knowing the detailed underlying geology takes this understanding to another level.

Our ancestors undoubtedly had a good understanding of the landscape, sometimes I believe they had a better understanding than many property developers have today.

I have just obtained another permission by offering to write a detailed report on the underlying geology of a farm and also do some free soil analyses. The farm has some fossiliferous rocks exposed on the land and I’m also going to identify the fossils and include them in the report with specimens for the farmer to retain.
XP Deus user.

All the gear but no idea !

User avatar
Allectus
Posts: 24592
Joined: Tue Oct 25, 2011 8:37 am
Location: Essexshire ;-)
Has thanked: 482 times
Been thanked: 2776 times

Re: Local Geology

Post by Allectus » Sat Mar 24, 2018 8:22 pm

You'll not find any more by knowing the geology of an area. x;

A ;)
British by Birth - English by the Grace Of God.

User avatar
Twit
Posts: 779
Joined: Thu Nov 23, 2017 7:00 pm
Has thanked: 1316 times
Been thanked: 525 times

Re: Local Geology

Post by Twit » Sun Mar 25, 2018 5:12 am

poly wrote:
Sat Mar 24, 2018 8:15 pm
I’ve been a professional field geologist / palaeontologist For almost 40 years and can only totally agree with all your comments twit.

I tend to read a landscape automatically, know the underlying rock types before even knowing the actual described geology just by assessing vegetation, soil structure and type, shallowness or steepness of slopes, overall terrain, field stones, presence or absence of running water, existence of springs etc.. Knowing the detailed underlying geology takes this understanding to another level.

Our ancestors undoubtedly had a good understanding of the landscape, sometimes I believe they had a better understanding than many property developers have today.

I have just obtained another permission by offering to write a detailed report on the underlying geology of a farm and also do some free soil analyses. The farm has some fossiliferous rocks exposed on the land and I’m also going to identify the fossils and include them in the report with specimens for the farmer to retain.
Thanks, I was starting to feel like someone who'd strayed :D. I only part studied geology for one year, but it was enough to introduce me to the field, and since then have picked up more information whenever I am drawn into its details.... sinking a well, a friend who collects gold nuggets, gardening, metal detecting, local topography and its history, and on and on. It is like that for me also - I walk into an area and before even thinking, I have assessed or sensed out around me in various dimensions, not just spatial or subsurface to some degree, but historical human presence also appears sometimes in its own way, as well as the state of the natural history around.

I am sure most animals have, and early humans had, a very strong sense of their surroundings - that from relying on knowing them instead of being focused on dominating them, and knowing them not in a way we imagine "knowing" in a superior learnt way , but instead by being very in touch by sense . I studied biology but dropped it after disagreeing with some of the approach, and just continued at a practical level with field work until taking up other directions...but I still look through an evolutionary lense at life around me ( including human) sometimes..... and it is really surprising how it all looks from that point of view . Other animals aren't stupid either they just don't formulate in the abstract so much, but they have the perception... even chimps can outsmart most people at memory games. :)

User avatar
Twit
Posts: 779
Joined: Thu Nov 23, 2017 7:00 pm
Has thanked: 1316 times
Been thanked: 525 times

Re: Local Geology

Post by Twit » Sun Mar 25, 2018 4:50 pm

Allectus wrote:
Sat Mar 24, 2018 8:22 pm
You'll not find any more by knowing the geology of an area. x;

A ;)
Come on Allectus :) , you must have detected a beach at least once ! That is like speeded up geology, where layers are measured in months or years, where items accumulate in natural pockets, where searching fresh sand will find you nothing but nothing but nothing. You don't detect rocky ledges where people don't go except for the sake of it, you choose areas where there is an entrance and bathing area to do better.... though you notice the modern area, do you notice the ancient one? Previously it was not bathing but a fisherman's corner you are looking for... so where is the old low water mark, where is sheltered from swell by underwater shallows etc. etc. etc.

Admittedly, someone methodically searching an area will do as well or better than someone who eventually covers the same ground " haphazardly", if only for the technique, but for someone like me with more space than can be searched, you try to figure out where is most interesting, testing the less interesting areas also as you go along ( because at the least you don't have a full idea of the substrate till you have dug a few holes) .

Geology comes into all of that - earth science/theory, and whether you are talking of sand or ancient layers of rock, hillside topology or gullies on the beach, it is still that. What geology isn't ( just) is sitting around giving names to stones - that is done to facilitate a higher discourse and reasoning. Some find it boring, but it only takes a little experience and imagination to catch the spirit of what it is about, and to open up a new world of understanding. The best place to learn is in the field, so us detectorists are well placed for that... out and about and often eyes to the ground - and when not, surveying the surroundings.

:)
Last edited by Twit on Mon Mar 26, 2018 4:35 am, edited 1 time in total.

poly
Posts: 49
Joined: Mon Dec 19, 2011 6:34 am
Has thanked: 28 times
Been thanked: 50 times

Re: Local Geology

Post by poly » Sun Mar 25, 2018 10:16 pm

Just emphasis the value of geology further, metal detectorists like archaeologists use geological analytical techniques in their assessment of new land, potential historic sites etc.. The first decision that is commonly made in any new metal detecting permission or archaeological investigative site is where to search, a decision that is based not solely just on historical records, the visible or underlying remains of a possible ancient construction (lidar interpretation) or by the previous discovery of artifacts but also by reading the current geological landscape (noting the existence of rivers, streams, springs, variation in slope, soil quality, soil features, type and depth, underlying and exposed rock type and assessment of apparent landscape changes over time). If it is a large permission covering many hundreds of acres with considerable landscape variation then all these factors can be come into play, however even if it is a single field permission then one or more of these factors might still be critical. You only need to look at old episodes of programmes like Time Team to see all these factors clearly being taken into account before a new trench is opened up for example ( and not just done by using geophysical data !). Simply google the term geoarchaeology to appreciate the importance of landscape analysis in any archaeological land assessment. There are numerous books on the subject plus site reports etc....

An understanding of all the fore mentioned factors allows the understanding and re-creation of the environment from the earliest time of occupation, the modelling of old / ancient land-use patterns together with an understanding of changes of land use and occupation through to the present day. The possession of such knowledge can only help with metal detecting, ie. allowing the recognition of potential areas of occupation or industry which one should try first.

Finally to give an blatantly obvious example; the specialist metal detectorist / gold planner searching for native gold whether flakes or nuggets does not randomly go detecting anywhere. A thorough knowledge and understanding of the exposed or underlying geology is critical, together with the analysis of rivers / stream sediment accumulations, strength of underlying currents, current eddies and slack areas, underwater potholes and the identification of ancient / fossilised placer deposits etc to name but a few features to be taken into consideration. This wealth of knowledge enables the detectorist / planner to have a complete understanding of the area under investigation and to determine where he / she should concentrate his / her searches giving him / her the best opportunity of finding those elusive flakes of gold.

Understanding the geology and reading the landscape is as critical to metal detecting as it is to archaeology. Will such knowledge allow you to find more artifacts - possibly through spending more time and concentrating ones initial efforts in likely hot spots. Will such knowledge have a negative affect - definitely not.

Sorry for meandering through this post.
XP Deus user.

All the gear but no idea !

User avatar
Phil2401
Posts: 1191
Joined: Sun Dec 04, 2016 3:31 pm
Has thanked: 684 times
Been thanked: 608 times

Re: Local Geology

Post by Phil2401 » Mon Mar 26, 2018 8:47 pm

Well I'm somewhere in between all that lot - in simple terms (I am simple) the folks of times past didn't just think 'this is a nice spot - we'll build a village here'.

As a local example, I live in Ewell, near Epsom. History back to pre-history, but the geology to a great extent explains why it has been inhabited for so long - water running down from the clay Downs hits solid chalk in Ewell and natural springs arise. What's the first thing you need if you're looking for a place to settle? a reliable supply of water. The earliest settlers looked for and recognised this (amongst other things).

Moving on a few eons in history, Stane Street took a turn here so the soldiers / horses moving between London & the south coast could take advantage of the natural springs - it's also about 15 miles from central Londinium - a comfortable day's march.

I'm not explaining this very well, but it seems to me that if you know something about the local geology, you can see why settlements developed where they did and why.

Phil
Quaerite et invenietis

Minelab Equinox 800
Deus Lite
Deeptech Vista Warrior

Garrett carrot
Fond Hope

User avatar
Twit
Posts: 779
Joined: Thu Nov 23, 2017 7:00 pm
Has thanked: 1316 times
Been thanked: 525 times

Re: Local Geology

Post by Twit » Tue Mar 27, 2018 1:34 am

In "my region" of Spain, basically a 5 by 10 km mountain backed valley, lined by hills to each side, there has been activity since pre-history. There is a similar water story to yours phil, the calcite (ancient seabed) mountain actually errupted, due to tectonics, through the surrounding later shale, it collects water that emerges year round around where it meets the shale on its lower slope, which happens to be where the oldest known sites are and a village is sited. You could look up "springs" and find them mapped, but without knowing how they work you would not really guess if they were ancient or not.

The town is called Mijas, which is derrived from "mines", and was mined pre-Roman... only a few mines remain documented... lead, iron, the Romans highly praised the marble from there and there is a quarry from the time on a hillside. The next mountain range, volcanic, several km further on, also has mines... I visited a mica mine, little more than a near invisible m2 of entrance tucked away in the middle of nowhere, that I am told was Roman.

So already there you have some clues.... but there was also a Phoenician / Iberian settlement by the shore, where the side hills meet the sea, eventually Romanised, Gothicised, Arabised, Conquistacised, and now Modernised, leaving little trace... the Moorish castle that the Vikings sacked to abandonment , a very few Roman ruins.... and the rest...the Roman coastal road ? A port ?

To get a clue here are references :

The river by written reference was used as a port.... but the river is dry ten months of the year, a mere flood channel ! No way to enter it even for sand.

So using a study from S France, med sea levels have barely changed in 2000 yrs... no good.

So to a study in Portugal of an estuary using core samples/ pollen count... early AD the whole flora changes from forest to grazing, due to smelting and agriculture, and the errosion due to this shows in the large estuary height increases caused by it in the core samples from then on.

Furthermore, test drilling for water shows the whole valley has been filled in.

Which explains how they found a Roman lead anchor 14 m down when drilling pylons for a highway, several hundred meters inland *.. in fact the completely bare unimposing juncture of two dry rivers where we used to hunt snakes, roughly 5 km inland , is considered to have been a loading area, or at least navigable.

Who would have thunk.

So this is just a small example of what information geology can bring... they are still guessing where the town was.... somewhere under layers of silt probably.... they are still looking for other towns also.... sometimes finding them using gradiometers .... even places like

https://en.m.wikipedia.org/wiki/Medina_Azahara

were completely covered and forgotten until more recently... after only a thousand years.

Maybe the point is that we should consider ourselves fortunate if we find anything at all !

* e.g. cited in https://www.unsoldeciudad.com/articulos ... l-ID6.html

User avatar
Phil2401
Posts: 1191
Joined: Sun Dec 04, 2016 3:31 pm
Has thanked: 684 times
Been thanked: 608 times

Re: Local Geology

Post by Phil2401 » Tue Mar 27, 2018 7:54 pm

With all due respect to Allectus though (and he's due a good deal of respect!)- he's absolutely right in the sense that you're not going to find any more than you would if you didn't know the local geology - you can spend many hours researching, be convinced that a particular spot is where people are most likely to have been, assume that this is where the finds are likely to be... and then find zilch (speaking from experience). Still have to walk over the target to find it. Knowing the geology is just one of many potentially useful tools - nothing more.

Phil
Quaerite et invenietis

Minelab Equinox 800
Deus Lite
Deeptech Vista Warrior

Garrett carrot
Fond Hope

User avatar
Twit
Posts: 779
Joined: Thu Nov 23, 2017 7:00 pm
Has thanked: 1316 times
Been thanked: 525 times

Re: Local Geology

Post by Twit » Tue Mar 27, 2018 11:15 pm

Phil2401 wrote:
Tue Mar 27, 2018 7:54 pm
With all due respect to Allectus though (and he's due a good deal of respect!)- he's absolutely right in the sense that you're not going to find any more than you would if you didn't know the local geology - you can spend many hours researching, be convinced that a particular spot is where people are most likely to have been, assume that this is where the finds are likely to be... and then find zilch (speaking from experience). Still have to walk over the target to find it. Knowing the geology is just one of many potentially useful tools - nothing more.

Phil
No disrespect was meant by me, and if you don't search you won't find. Actually finding objects adds to the geological view, if we look at it that way round, i.e. all the items I find tell me how that surface area has evolved - but it is no surprise that quite consistently most are within certain geological parameters, and because they have explained me those parameters , those are what I use, starting from a geological point of view. There really aren't any absolute rules though, as objects turn up in the most unobvious places also, so there is room for people to think and follow whatever view suits them best - who am I to say it won't be good for them? The first hammerred coin we found came in imported topsoil ::g

Post Reply

Return to “Research Section Forum”