Minelab Explorer Classroom Forum

Years ago, I was told by an old fellow that coins sink at the rate of about 1/16th of an inch per year, so in 16 years, one inch of depth. Now, I realize that this rate would be an average. It is based upon deciduous leaf decay, rain spatter of soil, etc., but I think it is fairly accurate. In the North Texas DFW area where I live, we have soil which contracts and expands creating gaps in the summer that you can just about drive a truck into (well a hot wheels anyway). That could be a mitigating factor in coin settle rate if the coin were to be positioned within a cracked area.

So, here is a discussion point for your consideration and input. Has anyone here ever seen or heard of a study which would quantify that rate? .0625 inch per year (1/16th of one inch)....at that rate, in 160 years, a coin would be at 10 inches, basically at the bottom of the depth range of most coils and users abilities. How about your personal experiences? What is it like in your area?

Certainly I have found old coins sitting on top of the ground. For instance, I recently found a 1910 wheat penny sitting on top of the ground at an old park, and my partner found a 1917 half dollar there at 6 inches depth, which would be about right for the settling rate. But the overall reality is that I think the number cited as a settle rate is fairly accurate for my area. Rocks, nails, other metals, occasional organic interference, these things might influence rate, but again, I think the rate is consistent enough to suggest coil sizes for use.

So, how about some discussion on this topic. What are your experiences, opinions, and based upon what?

HH,

Dennis

I think you have the jest of it. It all depends on the environment and size of the coin. Ive read the same thing, but there are soooo many factors not only natural, but man made changes. Anyone who says they know exactly how deep a coin will go is feeding you a line.... you have a good guessdament. Even freezing here in the north will move coins UP not down.. There are a ton of reasons i can give that change the depth of a coin. Now you may gain helpful knowledge by knowing your environment... like sand vs rock, how deep is the bedrock, trees in the area, do you notice changes in the soil that might tell you the soil been moved? Now what does surprise me is i find more pennies than dimes at the surface.... i mean in bare spots if it rains you can see them everywhere. Obviously, thats another discussion... one about denominations of coins in your pocket and detectors cherry picking the area. You have a good subject lets see where it goes.

Dew

wheaties sometimes have a layer of grass attached to the bottom, the grass for some reason does not rot when in contact with the copper. Have someone carbon date that grass and you have a scientific answer for your area. Or, you can just make educated guesses based on the wear on the coin.

I've found a few of the states quarters down six inches or more. The depth that they sink to seems to be related to how soft the dirt was and how many times they were ran over with the lawn mower.

DD

I think worms trapped in small grassy areas by roads and sidewalks make the coins sink really deep because the worms consume everything and then leave whats left over light and fluffy. In the old days they built many of the sidewalks on top of the ground above the grass, not level with sod like they do today, and the ground is bursting out above the old sidewalks today, so I think the coins are not only sinking but the ground has been rising also.

This is just my opinion - I don't buy the sinking coins theory. Here's why.

In order for a coin to 'sink', it must be surrounded by a soil matrix in a liquid state. How often are the areas that you metal detect in a liquid state? If you live in the snow belt, every spring as the ground thaws it is VERY wet for a short period of time. There are periods of torrential rains when flooding may occur causing the ground to be in a liquid state. But, for that vast majority of the year, the areas that most of us hunt are NOT in a liquid state that would allow the pull of gravity to force the ground matrix out from under the coin, ring or other item.

I think a better question is "How quickly does leaf, grass and other debris build up over time in the areas that you hunt?" Think about it and take a step back the next time you go past a park or an old home. How much 'build up' is there in the areas that are mostly stationary, like a sidewalk or a curb and gutter that surround a lawn. If you are looking at an old sidewalk or gutter, do you really think that the construction crew built that sidewalk 4 or 5 inches lower that the surrounding grass? No. Grass clippings, leaf debris, dust in the air, and whatever else the wind blew in slowly built up on the surface they landed on, becoming a new surface, growing up and up.

My house is 50 years old, and when I edge along my sidewalks, the grass in some areas is 3" higher than the concrete. Look at an original sidewalk around an old home and look how the yard has grown upward with the debris build up. In some of the older areas where I live, homeowners will actually bring in a bobcat with a front loader on it and scrape off several inches of buildup to get back to where the yard isn't sitting above the walkways.

Somebody mentioned finding wheaties surrounded by preserved grass clippings. I've seen this numerous times with pennies and nickels. Are we really thinking that the coin sunk down thru the dirt taking along a cocoon of grass with it? That doesn't sound plausible to me. It does sound plausible that the coin was dropped in the grass, grass clippings and thatch were under the coin, grass clippings and thatch and other debris fell on top of the coin slowly burying it. The coin protected the grass from the elements preventing it's decomposition into dirt. The build up continues over the years until you and I find that coin several inches deep in the yard of an old colonial home.

Coins aren't the only items that we dig up. If coins sink, we should be able to apply the same principles to other items. Do pull tabs and foil sink too? They don't seem very heavy compared to the amount of dirt they displace. Shouldn't they float in the dirt then? Why do I find pull tabs and wads of foil 3, 4, 5 and 6" inches deep along with coins? The sinking theory just doesn't add up for me.

I will concede that there are some mushy, soft areas that allow coins and other objects heavier than the surrounding dirt to sink until they find a bottom, but I don't think this represents the majority of our finds. Well watered parks and lawns will grow grass faster, which needs cutting more frequently, which will add cuttings and debris at a faster rate. Unwatered hardpan areas will grown less foliage and will be more subject to wind erosion removing debris thus allowing dropped items to remain on or very near the surface.

In conclusion, I think that debris buildup is the major contributor responsible for the 'depth' that we the targets we dig.

Again, JMO

Rich (Utah)

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etrac powered by RNB

I dont know about your area, but coins here in Indy do move or are moved and not just from soil build up. The roots, worms, freeze, man made construction, high water line, size of rocks and just really dry summers all cause dirt movement. That turns coins on their side and moves them up and down. When they start moving smaller targets tend to move.... much like gold moves down toward the bedrock as the dirt is shifted. Now in some areas they may not move as quickly as others like those in the south where they have a lot of clay. But in other places like Fl they move pretty darn quick. Put a small stone in a jar of sand and tap the side.... over a while it will move down because its heaver and gravity will move it. Shoot we get a few dry summers here and the foundations of homes move by collapsing of soil. Ive found clad at 6 inches... but most of the time i can tell the soil has been replaced and here there's a pretty obvious difference in soil layers. I dont think you can discount basic physics.

Dew

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Xcal II, Blue Xcal 1000, Exp SE
Those who know arent talking.... those who are, dont know.

Hundred year old parks with the roots of trees showing is proof that the soil hasn't "built up". Most parks have leaves and clippings removed anyway. I've dug farm tools at 12" next to the original house with the foundation showing (trees and grass in abundance). By the logic of above, the dirt would be 12" or more up the side of the house. You can look at 100 year old pictures of parks and see the same walls, sidewalks, trees, buildings etc that you see now but the silver is at 7". Once you get something under the turf, it sinks at varying rates depending on vibration, water, and composition, until it hits the harder layer, and I've never seen the dirt beyond 2" in these areas in what I would call a liquid state.

In the midwest, most areas have 12-14" of top soil and then clay. The oldest rocks and relics are sitting in the first 1" of that clay meaning things SUNK through that top soil - otherwise you'd have to conclude that roughly 220 years ago there was no topsoil - just clay, and everything was dropped on the clay and then plant life started decaying on top of it until VOILA 14" of soil 220 years later.

I'd say the 1/16th rule is accurate like 7 human years is to 1 dog year. It will apply in most situations but not necessarily because 1/16 if the correct number.

Here's another way of looking at it, The amount that they sink also has to do with the density of the soil, the density of the soil is a factor that effects depth too. A coin might sink fast in sand, but sand is the easiest for a detector to see through.

I believe it's a matter of where the target is and the amount of dead grass, leaf litter, silt(floodplain), etc. that builds up over them.

Other factors are:

- how much wind / precipitation erosion there is
- the grade and hydrology of the land itself

Coins at the top edge of the slope are typically shallower, coins at the bottom of a slope may be buried deeper due to soil eroding from above.

Of course, roots of growing trees and bushes and freeze/thaw cycles can raise up an object that was buried. I've found old coins laying on top of tree roots after a heavy rain.

Maybe metal objects will sink in very unstable sand.

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dewcon4414
I dont know about your area, but coins here in Indy do move or are moved and not just from soil build up. The roots, worms, freeze, man made construction, high water line, size of rocks and just really dry summers all cause dirt movement. That turns coins on their side and moves them up and down. When they start moving smaller targets tend to move.... much like gold moves down toward the bedrock as the dirt is shifted. Now in some areas they may not move as quickly as others like those in the south where they have a lot of clay. But in other places like Fl they move pretty darn quick. Put a small stone in a jar of sand and tap the side.... over a while it will move down because its heaver and gravity will move it. Shoot we get a few dry summers here and the foundations of homes move by collapsing of soil. Ive found clad at 6 inches... but most of the time i can tell the soil has been replaced and here there's a pretty obvious difference in soil layers. I dont think you can discount basic physics.

Dew

Hi Dew,

I hunt many different areas; ghost towns, parks, camping and hiking areas, old homes, schools, ski resorts and an occasional fresh water beach. In all the years I've been hunting (25+ on a more serious basis) I can only claim hunting a salt water beach 1 time.

I've seen this same discussion a number of times. IMO, I think a better way to look at it is "How do coins end up where they do?"

I agree with what you are saying above; there are an infinite number of outside influences that move or bury coins and other items we look for. But is it accurate of us to say that a coin covered with 6" of topsoil brought in as backfill or one that fell into a crack in the mud in the heat of summer in Texas 'sank' there. I don't think that's accurate. One was buried, the other fell into a hole. Neither really sank. Oft times beginners will get a false impression that coins sink into the depths of the ground like they are in quick sand and will keep going down like the titanic until they hit bottom somewhere.


Good luck out there,

Rich (Utah)

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etrac powered by RNB

Now that i agree with... how do they get there might cover it best. This is a subject that opinions count. I dont have your years of experience only about 15 now... but there arent very many states i havent hunted in. I traveled in an RV and metal detected full time for about 5 years..... when it got cold and i couldnt wear shorts i went south, i hate the cold weather when i cant hunt. Its great to bring up these questions i learn something every time.... in fact every time i hunt.

Dew

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Xcal II, Blue Xcal 1000, Exp SE
Those who know arent talking.... those who are, dont know.

I know people like to debate this subject, but if coins didn't sink shouldn't there be a layer of old preserved grass on TOP of the wheatie too if coins got depth by being covered up with grass clippings? After all, the copper would tend to preserve both sides of the coin.

Preserved grass on the bottom to me means that the coins sink, and they don't roll much while they sink either, they trap the grass at the bottom and the grass at the top sorta floats off.

I can often tell whether the coin I'm digging is going to be copper or silver. If I find a coin shaped matted bunch of grass it always means copper. Often this grass will cause the dirt clump to break up when digging leaving the copper coin exposed. Silver doesn't have the same preservative affect and often silver coins will end up in a dirt clump. I suspect many of you have seen the same phenomenon.

I posted a grass clump that surrounded a Large Cent I dug this spring. There was definitely grass top and bottom.

It seems this topic comes up often and is like creation vs. evolution or global warming, very passionate opinions. I firmly believe that coins do not "sink"; they get covered. Only when the ground is saturated enough to behave as a liquid would things sink. Some folks think that anything heavier than dirt is making a beeline for the bed rock. Then how come you find rocks in the dirt when you are digging?

From what I've read(and experienced) rule of thumb topsoil formation for mid west USA is 4 to 6 inches per hundred years. And as many have stated there are an whole lot of things that can affect the speed at which soil builds and even a greater variety of factors that can disturb this process, either leading to deeper or shallower coins.

I've found clad at 10" and seated laying on top of the ground; but in general this rule holds.

Chris