GeologyRocks

I'm afraid I can't help but I'm bouncing this in the hopes that someone more knowledgable will read it.

Hi Malcolm

I've got a few possible answers to your rocks. The first thing I thought when I saw them was that you might have had a lime kiln in the area. Limestone often acquires a powdery white surface deposit when it's been partially burnt, and this would also account for the quantity of loose stones just below the surface.

Other possibilities are that they could be mine spoil (any metal mines in your area that you know about?), a frost-shattered cherty bed in limestone, possibly glacial debris (but that would be low on my list), or the remains of a cairn.

Can you tell me what they look like when they've been smacked in half?

Gus

Thanks for your reply. The encrustation is powdery alright, but the limekiln idea doesn't fit because these rocks occur over a wide area. They can be found under every bit of green field that is left untouched in the village. We are talking about an area which would originally have been about 30 acres. I think there are only about 2 acres left untouched. The bedrock which is at or near the surface in all of the 'townland' of Bellanaleck is waulsortian limestone. It was quarried in several different locations. All the quarries are disused now. The geolgical map of the area shows an outcrop of the same rock about a quarter of a mile away in Mullymesker. I went to look for it and sure enough it was there at the surface, and without doing any digging, I found some of the same white stones lying on the surface. When one of the white stones is broken in half, the fine grained grey limestone typical of the area is what is revealed. I will attach a couple of photos. It is perhaps worth noting that fossils are standing proud of the surface of many of the rocks as if they have been weathered for a very long time. Maybe they were baked on the surface in desert like hot conditions for part of their history.
Photos will follow later(camera battery flat)

These photos don't make it quite clear enough, but the rock example shown has actually got a top,a bottom, a south side and a north side. The top and south sides are whitest, the north side is less white, but still weathered. The bottom is not weathered or white. This all seems to tie in with sitting in hot dry desert conditions for eons. Your mention of the lime kiln gave me the clue. Do you think this is the right scenario?

My opinion is that this is chemical weathering produced not by heat - but by water. Given the rock is a limestone, water is actually the main weathering agent.

The fossils may be more magnesium limestone rich, which is less prones to this kind of weathering, hence are standing proud. This makes sens as the bottom of the rock may not have had water running over it - hence is less "chalky" looking.

Having seen the new photos I'm inclined to agree with Jon - it's typical of limestones to have an "oxidised" surface due to surface weathering. I think you've put your finger on the amount of stones just below the surface - they could easily be quarry spoil scattered over a large area.

Gus

I agree that there was a lot of Quarrying done in the area. There was quite a bit of evidence of early quarrying activity here in the 1950's when I was a young boy. The quarrying was however very primative with very little mechanisation. There was an awful lot if it done by hand. ie sitting on a stone breaking rocks with a hammer. I just don't believe that any stone however small would have been discarded as spoil. The places where the white stones are found today are in the undisturbed fields. So in other words, I don't think they got there due to man's intervention. Because the area is not much covered with glacial till, I don't think glacial deposition was at work. More like the rocky plateau was scraped clean by the glacier. Under the fields that were recently excavated for building houses on, there was a graduation in the rock under the surface.Closest to the surface was the scattering of white rocks with the evidence of weathering, then below these were lots more rocks which were easily dug up and broken. These had no evidence of weathering. Below this was solid bedrock which had to have much more considerable force used to break through it. All in all, I think what we are looking at are very ancient layers. I'm not yet quite prepared to let go of the hot desert theory. I think the night frosts in the desert could have split the fairly solid rock up into smaller pieces, which then lay about the desert surface and got baked. I would be interested to know if there is any similar limestone lying around on present day deserts. By now I expect you've all had enough of white rocks!

Leave it to a prospector to dredge up an old thread like this!

I've uncovered rocks with a similar coating that came from a caliche layer. When I find caliche, I get excited because it usually indicates an ancient river bed. Caliche also acts as a sort of false bedrock, so if your in gold country, you can usually find fine placer gold above and within an inch or two of the caliche. The white powedery coating is calcium carbonate (I think). The rocks that I uncover are much more rounded than the ones you have shown, though, and they are usually accompanied by hard clay and gravels.