asking again because I know dick about coins/ detecting....
these coins eventually got washed out of a 300yr stationary position?
I mean being they were so close together and in great condition.
while rare, yes: This can happen @ beach erosion. And at first blush: It might seem strange that.... all of the sudden a strata is revealed that hadn't ever been revealed before. BECAUSE: There's been whopper cyclone storms that have hit the coast there, every 7 or 10 yrs. or whatever. Eh ? Thus *presumably* this strata or depth should logically have been reached before, thus mixing up all the targets (assuming the targets come back in , with the sand, during the spring/summer buildup of the beach-sand-migration).
But I have noticed that EVEN THOUGH WE HAD the "100 yr. storm" in 1982-83 on the west coast, and another whopper series of swells/tides during the '96-97 event, yet : There STILL continued to be beaches that had (and continue to have) new zones that seemingly were never reached in past events.
The reason for this is: That when the swells & tides and on-shore storm winds erode, they are not always eroding at the exact same spot. So, for example, at a certain given beach, in a certain erosion episode, the hot-spot may be a certain zone "here" and a certain zone "there". Yet not be the entire length of the entire beach. Then 2 yrs. later, erosion hits again, and the "hot spot" might be a block further down than the prior episode , in "all new sand".
Same for how-far-back into the dunes the erosion can affect : I have found silver coins that looked like they had come from land sites (ie.: never spent their life bathed in salt-water briny sand). This is because they got eroded out of dunes that ...... prior to this ... high-water events had never reached before. EVEN THOUGH PRIOR YEAR'S STORMS had been more severe. This is because mother nature doesn't always erode the same spots and dunes and cliffs, year after year. She develops different bees in-her-bonnet, at different locations, depending on subtleties of swell and wind direction of each event.
Lastly : Very heavy targets (like gold coins and fishing sinkers) move much less than lighter weight pennies/dimes. So when erosion has occurred, if any objects are going to be "stuck" at bedrock (assuming all the sand was washed out, leaving only cobble and tide-pools/rock), then: It's going to be the pennies and dimes that went "all the way out", and the heavier items that remain (since they're heavier and dense).
There was an episode like this in Monterey , CA a few years ago, where the resulting eroded surface looked like the surface of the moon: Pock-marked bedrock . And there was almost NO pennies/dimes there (and CERTAINLY no aluminum). The resulting items were strictly lead, old copper & brass hardware fixture junk, etc... And a $5 gold, etc...
Unfortunately, for the episode in Monterey @ the last paragraph ^^ , this happened at a beach that was used as a turn-of-century dumping ground for fill-dirt and municipal garbage (hence tons of lead and brass to wade through). But I can imagine that if this same phenomenon had happened at a strictly touristy beach, there would have been higher odds at gold coins. That had resisted all prior storm/erosion events, and remained stationary.
This is why gold coins, when found on the beach after erosion, rarely show evidence of having been "in and out" with the sand migration. Ie.: the effects seen on silver coins, where they are "sand-blasted", proving they've come in and out on the sand for decades. The 4 gold coins I've found after beach storms, on the other hand, were perfect. As if they'd never moved. DESPITE probable erosion at those exact spots (Ie.: they didn't necessarily "just fall out of the dunes").
Have I made any sense ? Does this answer your question ?