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Bob Shaw
post Jan 21 2007, 08:51 PM
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QUOTE (helvick @ Jan 21 2007, 08:18 PM) *
quote in reply! removed



Yup. As Dubya would have said, 'He's ma man!'. I have a well worn copy of 'The Principles of Physical Geology' sitting beside my desk even now...

The only flaw in his geological world-view is that he predated the serious study of impact events.


Bob Shaw


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tty
post Jan 22 2007, 07:48 AM
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QUOTE (Bob Shaw @ Jan 21 2007, 02:14 AM) *
Hmmm. And then got conveniently tilted 90 degrees... ...I have my doubts about some of this. It seems a bit much to invoke gradualism *and* catastrophism on one site (I remain an acolyte of Arthur Holmes!).


To me the layers look fairly horizontal and the bomb sag hypothesis is quite probable. The only other process I know of that can produce similar structures is glacial dropstones from icebergs that fall into soft bottom sediments. In both cases deformed rather than disrupted layers is quite common.

tty
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Bob Shaw
post Jan 22 2007, 08:59 AM
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QUOTE (tty @ Jan 22 2007, 07:48 AM) *
To me the layers look fairly horizontal and the bomb sag hypothesis is quite probable. The only other process I know of that can produce similar structures is glacial dropstones from icebergs that fall into soft bottom sediments. In both cases deformed rather than disrupted layers is quite common.

tty



Hmmm... ...I wonder what a cross-section below a rock which has migrated due to freeze/thaw processes would look like? Not that I'm seriously suggesting it as an explanation here, it's just that (now that I think about it) I've never seen such a thing, and presumably a lump of stone tunneling towards freedom ought to leave some sort of trail...


Bob Shaw


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ngunn
post Jan 22 2007, 09:13 AM
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QUOTE (Bob Shaw @ Jan 21 2007, 08:51 PM) *
'The Principles of Physical Geology' ...

he predated the serious study of impact events.
Bob Shaw


Aye, a venerable tome indeed - required reading when I was at school. Correct me if I'm wrong but I don't think he anticipated seafloor spreading and large scale horizontal movement of continents either.
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Bob Shaw
post Jan 22 2007, 11:14 AM
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QUOTE (ngunn @ Jan 22 2007, 09:13 AM) *
Aye, a venerable tome indeed - required reading when I was at school. Correct me if I'm wrong but I don't think he anticipated seafloor spreading and large scale horizontal movement of continents either.



Holmes was actually an early champion of Continental Drift!


Bob Shaw


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ngunn
post Jan 22 2007, 12:11 PM
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QUOTE (Bob Shaw @ Jan 22 2007, 11:14 AM) *
Holmes was actually an early champion of Continental Drift!
Bob Shaw


That I had either forgotten over the last four decades or never realised in the first place! Is that in the 'Priciples' or elsewhere? I'd like to revisit if you can point me in the right direction. Sounds like a trip to the library is called for. In my one-year encounter with the geology department at St. Andrews continental drift for the Earth and impact cratering for the Moon were both strictly off the menu, leaving me with the frustrating impression that geologists in general were in perverse denial about the most significant (and visibly obvious) morphological processes on both worlds.
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Bob Shaw
post Jan 22 2007, 01:19 PM
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QUOTE (ngunn @ Jan 22 2007, 12:11 PM) *
That I had either forgotten over the last four decades or never realised in the first place! Is that in the 'Priciples' or elsewhere?


See Helvick's post #585 above!


Bob Shaw


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ngunn
post Jan 22 2007, 01:50 PM
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QUOTE (Bob Shaw @ Jan 22 2007, 01:19 PM) *
See Helvick's post #585 above!
Bob Shaw


Thanks Bob and Helvick. Everyone else - sorry for the unmartian diversion. Off to the library I go (or maybe the second hand bookshop) to re-learn what I must have unlearned in St. Andrews. An unexpectedly fruitful outcome from my feeble attempt at humour . . . Sheer luck Holmes!
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atomoid
post Jan 24 2007, 12:35 AM
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QUOTE (Bob Shaw @ Jan 22 2007, 08:59 AM) *
Hmmm... ...I wonder what a cross-section below a rock which has migrated due to freeze/thaw processes would look like? Not that I'm seriously suggesting it as an explanation here, it's just that (now that I think about it) I've never seen such a thing, and presumably a lump of stone tunneling towards freedom ought to leave some sort of trail...
Bob Shaw

er yeah, one would similarly wonder if impact ejecta could give a similar appearance if it fell onto a muddy plain... no volcanic origin necessary... just a terrestrial rock, perhaps by chance even originally volcanic, but sunk into the soft layered sediments completely via non-volcanic (or even as thrown about in this thread, freeze/thaw or glacier) processes. how could we tell the difference?
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ElkGroveDan
post Jan 24 2007, 03:29 AM
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QUOTE (atomoid @ Jan 23 2007, 04:35 PM) *
but sunk into the soft layered sediments completely via non-volcanic (or even as thrown about in this thread, freeze/thaw or glacier) processes.

....or even as a byproduct of mass wasting from a steep cliff or hillside; bounce, bounce, bounce, thud!

note the carefully culled quote wink.gif


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CosmicRocker
post Jan 24 2007, 06:22 AM
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In the end, this thing can be explained using a number of familiar earthly processes if we only consider the physical appearance in the images. I can't remember where, but I recall some official mention of spectrometry supporting a classical volcanic composition over the entire thickness of the stack here. Though not definitive, that would seem to tilt favorably toward volcanic physical processes being involved in the origin of these rocks. The aeolian reworking of the upper section really threw we for a while, but I am beginning to see that there are a number of ways to look at the information we have.

The sub-discussion of some of the founding concepts of modern geology (and indeed, many other sciences), reminded me of the "standing on shoulders" concept that is often mentioned when major advances in science are discussed. Hutton's gradualism, Lyell's uniformitarianism, Bretz's catastrophism...you can argue over who first proposed some of those concepts, but in the end it all depends on many people collaborating over time.

That is what I find so interesting about our current situation. We find ourselves exploring an alien world, trying to imagine it's origin and history, and realizing that the philosophy of science that we created on our world can be extended to others. We are here collaborating. Could life be better?


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tglotch
post Jan 25 2007, 08:56 PM
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QUOTE (CosmicRocker @ Jan 24 2007, 06:22 AM) *
I can't remember where, but I recall some official mention of spectrometry supporting a classical volcanic composition over the entire thickness of the stack here. Though not definitive, that would seem to tilt favorably toward volcanic physical processes being involved in the origin of these rocks.


The Mini-TES work that Steve Ruff has done indicates that Home Plate has a large component of volcanic glass, supporting the volcanic hypothesis.
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