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985 Views 12 Replies Last post: Oct 29, 2013 3:31 PM by tjharte RSS
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Oct 28, 2013 9:00 PM

what are the layers of this soil and what age ?

i was out with my freind on the bulding site in wigan,highfield  in began to rain and the water drained into the brook below is deposited sand and cut through layers what are the layers of this soil on the pic. and why does it depoisit sand and was the brook made this way and what was the habitait when the brook was made and what lived there

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    Oct 28, 2013 9:10 PM (in response to tjharte)
    Re: what are the layers of this soil and what age ?

    I have no idea what layer it is, but all of the rocks in Wigan are carboniferous in age.  Pic 2 looked like a man made rock, but from some of your previous posts I have seen you have found some nice pieces of fossil wood.  On some of the other pictures the wood looks like it is in carboniferous cole formation.

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        Oct 28, 2013 9:39 PM (in response to tjharte)
        Re: what are the layers of this soil and what age ?

        340 million years ago the whole of Wigan and a lot of Yorkshire was covered in forests.  Giant insects lived there like 6 foot centapedes, 1m scorpions and loads of other huge insects like giant dragonflys.  But don't expect to find fossils from them because they are very rare.  When I went fossil hunting In a stream I found a fossil root and a smaller piece, but I much prefer to go hunting in my usual spot which is full of them.  Anywhere you can find coal you can find plant fossils because coal is made from prehistoric plants.

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      Oct 28, 2013 9:39 PM (in response to Dan)
      Re: what are the layers of this soil and what age ?

      The brook is relatively recent (thousands of years, say).

      It will have been washing sediment downstream most of that time. Wherever the slope of the river bed decreases, the speed of flow will also decrease, and that will cause particles of sediment (that were suspended in the flow) to be dropped. That causes sediment to build up and consequently the stream to adjust its course - which may enable it cut through some earlier sediment, perhaps steepening locally, pick-up sediment again, and keep it suspended for a while. The cycle repeats countless times in different places across and along the stream.

      So, if you were to follow the water downstream and/or follow it over the days and years, you would see the stream bed was in a continual state of reworking. That also involves cutting into fresh parts of the river bank and river bed, exposing new soil and/or rock, and adding particles to the flow.

      Your last photo shows the stream is very wide and shallow. One might expect it to flow as a thin and even sheet of water, but nature has other ideas... In this sort of situation, a stream/river becomes intricately braided (Google 'braided river').

       

      Your stream seems to be cutting into banks made of a composite soil which may be partly man-made. The angular stones look like aggregate, such as that used for railways or road construction. Such aggregate can occur naturally, too, but my feeling is that it is man-made in this case.

       

      Imagine that soil once it has been washed into the stream. The flow will separate the larger and smaller particles, depending on the rate of flow and the particle size, shape and density. The larger and denser pieces will be dropped more readily than the finer particles. Then, where you get accumulations of sand it is just because there was sand in the bedload or suspension, and the speed of flow reduced sufficiently for the sand to be deposited. A similar thing can be said for areas of silt, and areas of mud - different particle sizes being deposited (or picked-up) according to the flow regime.

       

      What lived there?

      Probably much the same as lives there now.

       

      Mike

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