What is cross-bedding? A basic geology course might explain cross-bedding in this way:

The second feature of sedimentary rocks is called cross-bedding. As clastic sediments are transported by water or wind, they form sand waves. The image [above] shows this process for wind-blown sand. In figure 1, the sand wave can be observed. As the wind blows, it picks up sand particles from the rear of the wave, and deposits them over the leading edge of the wave. This process can be repeated, making a wave on top of a wave, as in figure 4. These waves can range in size from small ripples only a centimeter high, to giant sand dunes hundreds of meters high.

The structure of the bedding tells us the direction of the wind that deposited the sand. Figure 7 in the above diagram shows the wind direction for each cross-bedded sand wave. By the size of the cross bedding and the angle of the bedding, you can also tell if it was a beach deposit or a wind deposit in a desert environment.

Seems pretty straightforward, doesn't it?

One typical example of cross-bedding that Young Earth Creationists point to is the Coconino Sandstone in the Grand Canyon. The argument, as I understand it, is that the angle of the cross-bedding is a bit lower than one might expect were it the result of wind deposition — the Coconino cross beds are inclined at about 25 degrees, while most wind-deposited cross beds are at 30 to 34 degrees.

Of course, what isn't mentioned on, say, the Answers in Genesis explanation, Young Earth explanation the cross-bedding is that water-deposited cross beds rarely exceed an angle of 10 degrees. And upon closer examination of the specific sand which forms the Coconino cross beds, one observes that the authors of the Answers in Genesis article ommitted more information than just this

[Steven A. Austin] argues that the angle of the slope of the cross beds indicates an origin other than eolian [wind-based processes -- Ken]. He claims the average angle for Coconino cross beds is about 25°, which is less than the average angle of slope observed in sand dunes today. He states that sand dunes today exhibit angles as much as 30°, and even up to 34° (notice he doesn't actually give the average angle observed today). By contrast, oceanic sand waves are less. However, as one of my readers has noticed (thanks David), a casual reading of geologic literature shows records of wind-deposited cross beds which are as low as 10°. They have been found to range from 10° to 34°, but typically, they average between 25° and 28°.

Austin fails to tell the reader all the information (a typical young-earth tactic). By contrast, water deposited sand is rarely steeper than 10°. When he claims that water-deposited cross beds are less, he fails to tell the reader by how much. Since the Coconino's cross-bedding is 25°, they are obviously wind-deposited. They fall within the average for eolian cross beds (25°-28°), but are far from the angle expected for water-deposited cross beds (less than 10°). Had Austin included the actual cross-bed angles for water-deposition, it would have ruined his argument. Thus, we see the trickery that he has to resort to in order to deceive his readers.

Indeed, to believe Austin's Young Earth model of sand deposition at Coconino, one would have to believe that "a 30 foot tall sand wave can be moved over 400 miles in less than a week, with a current of only 5.5 feet per second." This is more or less impossible, even if one only pays lip service to the laws of physics in one's calculations.

And that doesn't even begin to get into the discussion of how water, moving at about the same speed that human beings can walk at (if the water's speed was faster than about 5.5 feet per second, cross beds would not be formed), could have eroded the 11,931 cubic miles of sand from other places and deposited it in the Coconino beds in the short amount of time that it took for the flood waters to recede, per the Book of Genesis. By that kind of logic, Hurricane Katrina should have re-located New Orleans to Arkansas.

So let's go back, again, to what I said before: deep cross-bedding (Coconino is a large geological formation) does not mean what Andrew thinks it means. The presence of deep cross beds is actually an argument for a very old Earth, in which wind deposition of sand has shaped, over millions of years, some truly impressive geological formations.

Now, I haven't addressed all of Andrew's points, but I have covered the substantive ones. I'm sure that were I to dig into what claims I have left unanswered, I would find still more examples of this pattern…but I think this post is getting long enough as it is. Be that as it may; within the scope of what I have covered, we can see a consistent pattern emerging: each argument which Andrew asserts is demonstrative of a young Earth is, in fact, demonstrative instead of a very old Earth, and then one in which a global flood did not occur.

This does not, however, undermine the validity of the Bible or the message of faith which is imparted to humanity through the flood accounts.

"To conclude, Scripture and science do not support the historicity of [the flood] as described in Gen 6-9. Of course, every Biblical author believed that [Noah] existed and survived a world-destroying flood on an ark. But this was the history-of-the-day for the Jews and early Christians. At best, Noah points back to an obscure individual/s who lived through a local deluge/s, most likely in the Mesopotamian flood plain. But more importantly, the iblical flood is an incidental vessel that reveals the inspired message that God judges sin and saves righteous individuals from His wrath." (taken from: Dr. Denis O. Lamoureux, Evolutionary Creation, pp. 280-281)

The exact historical details aren't the important aspects of the flood accounts in Genesis. Yes, the authors of the text of Genesis believed that these were real events which had transpired, but the authors themselves weren't present for the flood even if it did happen, so how could they be sure? Moses, traditionally held to be the author/redactor of Genesis, was not present for the flood even if it did happen, so how could he be sure? He would have had to rely on the oral traditions of the Hebrew people, oral traditions which were informed by ancient, experientially-derived primitive science, which could not perceive even that the Earth was in orbit around the Sun, let alone the subtle clues as to the Earth's actual age.

And here's another consideration: from what we know from Scripture, even if Noah did exist and did survive a catastrophic flood of global proportions, he didn't seem to bother taking any extant historical records with him into the ark; to assume otherwise is eisegetical. So if the Young Earth Creationists are correct, and if the flood that Noah weathered actually did happen, the assumption that the earlier chapters of Genesis give an accurate historical picture must be discarded, since no records from before the flood could have survived. Only oral tradition and word-of-mouth would have existed to pass along the pre-flood history to later generations.

I trust that the good Reader has played the telephone game before.

For the Spirit, who inspired the authors of Scripture, though, the fact that the authors were retelling an ancient historical legend rather than the actual history of the world wasn't the important part. The Spirit, accommodating to human ignorance, worked through those historical legends to impart to humanity a message of faith.

Minor Update: for those who might be interested, Mount St. Helens is also not actually evidence of a young Earth.