[Rockhounds] glacial erratics (was Stonehenge geology resolved)

[R. Peter Richards]

Apologies to Lanny, who said pretty much the same thing I said.   
Guess I read his post too fast!

Pete Richards

On Feb 2, 2009, at 12:49 PM, R. Peter Richards wrote:

> Since it is a sedimentary rock (albeit perhaps a metamorphosed  
> one), the details of the thickness and texture of the beds should  
> answer this question.  If both pieces are part of the same rock  
> originally, the bed thicknesses and grain sizes should match  
> closely from one to the next across the split.  If they are just  
> two rocks that happened to wind up next to each other, there is no  
> reason that these characteristics would match nearly as well, and  
> they might not match well at all.  Unfortunately, one cannot judge  
> this from the photograph, but I would have to guess that someone  
> has applied this test.
>
> Pete Richards
>
>
> On Feb 2, 2009, at 12:13 PM, Lanny R wrote:
>
>> I have a doubt about the "Big Rock," this Okotoks Erratic really  
>> being one rock broken into two pieces. First, I don't recall ever  
>> seeing a large rock that I was sure had obviously broken into two  
>> pieces where it had settled in the middle so that the two pieces  
>> dipped inwards. Secondly, I can't see any match in the layers  
>> between the two pieces. That might be just a problem of how it is  
>> shown in the photograph, so that one can't really see them all  
>> that well. Thirdly, the piece on the right is more broken up and  
>> has a lot of  rusty layers, very unlike the left piece.
>>
>> Any others care to express their opinion on this?
>>
>> Regards,
>>
>> Lanny
>>
>>
>> On Feb 2, 2009, at 8:48 AM, pmodreski at aol.com wrote:
>>
>>> Neat website about that big rock, Kreigh!
>>>
>>>
>>> Some erratics are big. You might enjoy the size of the biggest one?
>>> ?
>>> http://culture.alberta.ca/museums/historicsiteslisting/ 
>>> okotokserratic/default.aspx?
>>> ?
>>> and the interesting legend of how it split in two.?
>>> ?
>>> Kreigh?
>>>
>>>
>>> And, alas, I'm afraid your post was a great disillusionment to  
>>> me, because I couple of years ago I had visited, and was very  
>>> impressed by, the Madison, Carroll County, New Hampshire, glacial  
>>> erratic, a N.H. State "Wayside Monument" and locally known as  
>>> "the largest known glacial erratic".? It is,
>>>
>>>
>>> "Madison Boulder is a huge granite rock measuring 83 feet (25 m)  
>>> in length, 23 feet (7.0 m) in height above the ground, and 37  
>>> feet (11 m) in width. It weighs upwards of 5,000 tons."
>>>
>>> Your Okotoks Erratic "Big Rock" in Alberta has?clearly got it all  
>>> beat,
>>>
>>> "The Okotoks Erratic weighs 16,500 tons. It measures 9 metres  
>>> high, 41 metres long and 18 metres wide."
>>>
>>> and?evidently holds the world record, as is stated in the very  
>>> good Wikipedia article about glacial erratics,
>>>
>>> http://en.wikipedia.org/wiki/Glacial_erratic
>>>
>>> Next time I'm in Alberta (never been there, actually), I've got  
>>> to see it!
>>>
>>> Cheers, Pete
>>>
>>>
>>>
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> ___________________________________
> R. Peter Richards
> rpr at heidelberg.edu
> Morphological crystallographer
>
>
>
>
>
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___________________________________
R. Peter Richards
rpr at heidelberg.edu
Morphological crystallographer





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