Thursday, April 19, 2007

More on geoglyphs

This is a subject about which there is dis-agreement. However, Norman Muller wanted me to add this.

Here is an explanation of what those curious weathered formations at the Miner farm and elsewhere are called. They are not geoglyphs but autoliths. Herman Bender provided me with the following explanation:

It took a bit of digging in my geology library, but I found it! The best term used to describe these rounded masses that weather out is : autolith - 1) an inclusion in an igneous rock to which it is genetically related Cf: xenolith, Synonym: Cognate Inclusion. 2) In a granitoid rock, an accumulation of Fe-Mg minerals of uncertain origin which may appear as round, oval or elongate segregation or clot. What it all means is that the 'round segegration' can be so close to the parent rock in lithology that it is barely indistinguishable and weathers out with Fe or iron present.

Hermann adds:
I as a geologist, have seen hundreds of these in nature and instinctively knew they were natural, a product of magmatic differentiation (i.e. an autholith) and in some other cases rheomorphic flow.

3 comments :

JimP said...

I'll wait to find out what geologists who have actually studied the formations in person have to say. I personally have already heard from two separate geologists who both given independent preliminary opinions from photographs that the single circle at the Miner Farm is likely manmade.

I have also seen the photocopied images from the article Norman sent me. While those images appear slightly similar, they don't seem to me to be the same to my eye as the single circle at the Miner Farm.

This debate cannot be settled without proper field study from qualified experts.

pwax said...

The question is easily settled by anyone who has the time and money to do this: cut one of the rocks in half and look for iron circles on the inside. [I do not mean any of the "famous" rocks, but I gather that there are lots of them in this area.]

Different people, qualified or otherwise, can give their opinions but what is the point of arguing when there is a definitive experiment which would settle it?

JimP said...

You're getting no argument here from me. To be quite clear, the argument is between one geologist who has seen some photos, and several other geologists who have conducted field studies. As far as I'm concerned, any debate on here that excludes a qualified geologist is pointless.

I also believe this is much more complex than can be settled by simply cutting a stone in half. There would be debate over which stone should be cut. Then there would be discussion over whether the sample stone is similar enough to create a definitive answer for all the formations in all the stones.

Not all of these formations are alike -- the weathered formations on Millenium Rock are different from the figure-8 on the Miner Farm, which is different from the single circle on the Miner Farm, which is different from the shaped effigy boulder on the Miner Farm, which are all different from the ovals on Ekonk Hill.

The presence of obviously worked boulders at the Miner Farm, including those worked for quartz quarrying, should be enough to sway the benefit of the doubt in favor of petroglyphs until a more definitive answer can be established by experts in the field.

But then again, you guys don't believe the experts on Yawgoog or Ekonnk Hill, so I guess we'll go around in circles forever on this one.