cannon ball?

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cannon ball?

Post  tottingtonroadcannonball? on Sat Nov 14, 2009 2:12 pm

HI

I've found a small stone (possibly quartz) sphere whilst digging in the back garden, Tottington Road, Bury. Could it be a cannon ball? It is about 2 inches in diameter, but not perfectly spherical. Kirkless brook is adjacent to where I found it so it could simply be 'eroded' by the water I suppose. Is this of any interest to anyone in your society? Do you know of any similar finds?

Apologies for bothering you and thanks in advance for any information.

Regards
Paul Birkett

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an update on the 'cannon ball'

Post  tottingtonroadcannonball? on Sat Mar 27, 2010 12:55 am

Hi

I am not sure if this is of interest as I've not had any information from the forum but I have been able to find out some more about the 'cannon ball'. My uncle, John Varker, is a (now retired) professional geologist and had a look at the rock for me. I copy his summary (which is more geology than history) below which he has kindly said I can publish here. His conclusion is that it is possible that the rock was used as ammunition of some sort, but the more likely explanation is that it
is just an erratic. However, I am still interested in finding out a little more
about the history of the Bury area, especially during the War of the
Roses, and in particular anything related to fighting in the area. I
understand that the Pilkington Manor House/castle was raised to the ground at
some stage and wonder whether there was any fighting at this time. I
also understand that one cannon ball was found at the 'castle/manor
house' site. What size, and type of material was this? Is it available
for viewing somewhere? Can anyone recommend any good books on the history of Bury or more particularly the manor house/castle.

Here is the report:






"I have had a good look at the cannon ball through my
binocular microscope, and have more or less confirmed what I thought about it
from my cursory examination on Leeds station, the first
time I saw it. It is indeed a granite,
more specifically, a fairly coarse, uniform, granite consisting of:-


Quartz – these crystals are mainly small and interstitial,
being normally the last mineral in the line to crystallise. These are essential for the rock to be a
granite. The percentage occurrence may
be a bit higher than usual, and whilst the majority of crystals are small, a
few are larger and subhedral, possibly indicating an interrupted cooling or
even several phases of crystallisation.


Felspar- as you probably know, this is a complex mineral
family. The K felspars (orthoclase) do
not appear to be present (would need a thin section to confirm this). They would be identified in hand specimen by
their 900 cleavages, and whilst they are often pink, this is not
necessarily so. The felspars in your
specimen appear to be all plagioclases ( a solid solution series albite to
anorthite – Ca to Na and distinguished in thin section by their changing angle
of cleavage). These are the white
crystals, which are laths in shape and with an obvious cleavage parallel to the
long crystal boundaries. Their almost 900 cleavage angle and
white colour suggests that they are most likely at the albite end of the
series, but there are many exceptions to these general rules. Felspar normally constitutes about 40 to 50%
of the whole in a standard granite.


Mica – again a complex family. The common one, almost always present in
granites is biotite, which is brownish in colour but can look silvery in thin
cleavage flakes, or when it has undergone chemical change during weathering. Far less common in granites is muscovite,
which always glistens silver in appearance.
I think both may be present in this sample, which would make it slightly
unusual.


I showed the specimen to a friend of mine who is a
specialist igneous petrologist. She did
not feel able to say with any authority where it had originated; it is not
particularly distinctive. The only way
to be sure would be to have a thin section cut or one of several chemical
methods of analysis, any of which would damage the specimen, so I said no to
that. If you were ever to find another
specimen that could have a thin sliver cut from it, I think that she would be
willing to have a closer look at it out of interest.


So, if you want an actual name for the specimen, how about –
A medium grained, uniform (no flow textures – bearing in mind that it was
originally a liquid), leucocratic (poor in ferromagnesian minerals that are
generally dark in colour) granite.


This rock has definitely not come from anywhere near
Bury. The Lake District
granites (there are several) are the closest geographically, but they are all
related to the Shap Granite with its large pink orthoclase feldspars. Since there are no pink feldspars in this
specimen I think we can rule out the L.D. completely. That brings me back to what I said last
time. Its most likely provenance is one
of the granites in the North West Highlands of Scotland,
but as I also said last time, Norway
is also a possibility. In either case, I
would think that the shape originated as a beach cobble, since prolonged
grinding in the waves can produce pebble and boulder beds of surprisingly
perfect spherical shapes. These
pebbles/cobble/boulders (defined size parameters) were then picked up by the
ice sheets that are known to have come down the west side of Scotland on many
occasions (now know to have been up to about 50 separate ice advances during
the last 2 million years, of varying severity).
Distinctive western Scottish marker rocks (erratics) of Ailsa Craig
microgranite, for instance (this is the one used to make all of the world’s
curling stones and occurs on one tiny island – a volcanic pipe about 300 metres
in diameter, in the Firth if Clyde) and others are found in the boulder clays
left by the ice all over Northern Ireland, The Isle of Man, Lancashire and North
Wales. With these it is possible to
determine precisely where the ice came from. When the ice melted each time, it
left behind all of the debris that it had carried – which is what the boulder
clay is.


The Norwegian connection is less likely I suppose but is
exactly the same story, except that the boulder clays containing several
distinctively Norwegian rock types occur down the East coast of Scotland
and England. I suppose it is conceivable that if it was
used as ammunition that it was carried from places like the Holderness coast to
use in the Bury area. My colleague at
the Dept suggested that it could be useful to find out where the different ‘warring’
factions came from if there was any fighting in Bury.


So I think that the most likely explanation for your piece
is that it was collected from the boulder clay somewhere in the north west of
England, or that it was washed out of the boulder clay naturally by river
erosion and collected from a pebble/boulder bed in some local river valley.


I feel that the hardness of granite and the lack of
mechanical means to make the ammunition (am I showing my ignorance here?) must
surely point to the shape of the cannon ball being natural. You mentioned scratches on the surface. I did
not really see any, but even if they are there, they would be just as likely a
product of natural erosional effects upon a beach, as some manmade artefact.
Dr John Varker"

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