From "Rock of Ages" by Frank Zindler
Most creationists try to follow the biblical scenario of creation, fall, flood, etc., as literally as possible. This means that they must do everything possible to discredit the notion that the earth is millions, nay, billions of years old. This is so because the chronologies recorded in the Bible imply that the world was zapped into existence around the year 4004 BCE - give or take a few months.  To save the biblical chronology, it has been necessary for creationists to attempt a reconstruction of the entire science of geology.
The facts of nature, however, are quite insistent: they tell us the earth is old. Some of the evidence is so clear and unequivocal that even persons untrained in the sciences can understand it as soon as it is presented, and they can see at once that it deals a fatal blow to the biblical chronology.
One such evidence derives from rocks which exhibit unusual structures called varves. Varves are thin, laminar structures that, when seen edge-on, resemble the growth-rings of trees. Typically, each varve is comprised of a couplet of light- and dark-colored layers of material. In true varves, each couplet of layers represents material laid down under water in a single year. Like the growth rings of trees, the laminations in varved rocks record an annual climatic rhythm. In northern lakes during the spring and summer, because of wave action, only large particles can settle to the bottom to form a layer of sediment. In winter, however, when the lakes freeze over, even very fine particles (including much of the organic material) can settle below wave-base and form a second, darker layer.
The proof that varves represent annual deposits can be quite compelling. N. J. Berrill, in his book Man's Emerging Mind, tells of a varved shale from the Miocene Epoch of Switzerland:
Certain shales of Miocene age in Switzerland bring that ancient world as vividly to life as any poster advertising the glories of a Swiss canton. For layer upon layer repeat the following sequence: compressed in the bottom of each layer are the blossoms of poplar and camphor trees, symbols of spring; immediately above is a thin region containing winged ants and the seeds of elm and poplar, all of summertime; and this in turn is overlaid by the autumn fruits of camphor, date-plum and wild grape. The whole progression of the seasons, year after year, are there in the earth like an enchantment. Time past was as real as time present. It should not be thought that Berrill's example is a unique or isolated example. Richard Foster Flint, in his famous textbook, Glacial and Pleistocene Geology, describes more modern varves ("rhythmites") that have been studied in Switzerland:
Rhythmites deposited in a lake near Interlaken in Switzerland are thin couplets, each consisting of a light-colored layer rich in calcium carbonate and a dark layer rich in organic matter. Proof that these rhythmites are annual and are therefore varves is established on organic evidence. The sediment contains pollen grains, whose number per unit volume of sediment varies cyclically, being greatest in the upper parts of the dark layers. The pollen grains of various genera are stratified systematically according to the season of blooming. Finally, diatoms are twice as abundant in the light-colored layers as in the dark. From this evidence it is concluded that the light layers represent summer seasons and the dark ones fall, winter, and spring. Counts of the layers indicate a record extending back to 9,500 yr B.P. ["years before present"]. Since the latter set of varves are at least 3500 years older than the earth itself, according to the biblical chronology, they must surely be a work of the devil, and it would behoove all profit-making prophets in the Land of Creationdumdum to do everything possible to explain them away.
One of the first to attempt this Everest of biblical apologetics was John Morris' father, Henry M. Morris. In my opinion, Morris père is the person most to be blamed for the recrudescence of creationist pseudoscience in the space-age. In 1961, along with coauthor John C. Whitcomb, Jr., Morris published the creationist "classic," The Genesis Flood: The Biblical Record and Its Scientific Implications. That was the volume of tomfoolery that formed the basis for what is wishfully called "creation science," an attempt to make biblical myths look and sound scientific.
In that never-revised book, Morris and Whitcomb devote eight full pages to the explaining away of varves. Citing genuine scientific authorities on peripheral issues, they attempted to cast doubt on the thesis that the pairs of layers in varved sediments are annual in nature. But do Morris and Whitcomb have an explanation for Flint's pollen data? Do they even mention it? Of course not - even though it is certain that they have read Flint's book, since they cite it in their critique. The Interlaken deposits are ignored totally. And well might they ignore them, since they could not possibly explain them away. Still less could they end their general discussion of varves with the conclusion:
Thus, it is concluded that the varved clays of the Pleistocene glacial lakes offer no problem to the chronology of Biblical geology. The varves were deposited, either annually or at shorter intervals, within the post-Deluge period. This would not compute if they had to include the 9,500-year record of the Interlaken varves. According to the Hebrew chronology, Noah's flood occurred in the year 2,348 BCE.  Since Morris claims varves to be post-deluge, we have a serious contradiction here. The flood would have had to have been much earlier than the biblical chronology implies. Furthermore, since the Hebrew chronology dates the creation at 1656 years before the flood, if we combined the varves with the pre-flood biblical chronology we would have creation at around 11,000 BCE. - fully a thousand years earlier than the most daring of the seers at ICR would allow! 
In what would appear to be a deliberate attempt to obfuscate the varve evidence, Morris and Whitcomb quote from my old geomorphology professor, William D. Thornbury:
There has been criticism of this method of arriving at estimates of Pleistocene chronology. In the first place, it involves a great deal of interpolation and extrapolation, which introduce possible errors. Secondly, there is some question as to whether varves actually are annual deposits. Deane (1950) from his study of the varves in the Lake Simcoe region of Ontario was led to doubt seriously that varves represent yearly deposits and was more inclined to think that they represent deposits of shorter lengths of time. From personal experience, I know that Professor Thornbury accepted the Swiss varves mentioned earlier as being true annual deposits. In the passage quoted, he was dealing mostly with the problem of correlating varve deposits in one part of the world with those somewhere else. As for the idea that varves in general represent deposits of less-than-annual periodicity, we note again that our Christian authors have left out the conclusion of the passage quoted. Thornbury ended the above passage with the statement that
Results from radiocarbon dating of late Wisconsin deposits are not in complete agreement with ages arrived at by varve counting but are similar enough to suggest that varves are probably annual deposits.It was necessary to leave out Thornbury's conclusion mentioning radiocarbon, because on page 423 they would make one further attack on varve chronology:
The highly doubtful significance of any varve chronology has been demonstrated plainly in recent years by its general rejection by geologists when the newer radiocarbon method was found to be contradictory to it.Further insights into the methodology of Christian geology as practiced by Morris and Whitcomb can be gained by noting the fact that on the page preceding the above conclusion they quote from Flint's Pleistocene Geology (as we have noted, without mentioning Flint's dramatic description of the Swiss pollen sequences) appearing to cast even more doubt on the annual nature of varves and to imply that Scandinavian varve studies are in disarray. Left out of the quotation, however, is a part saying that the varve chronology is widely accepted in Europe, and that there is radiocarbon support for it!
Can it be an accident that this line was omitted?
While it is true that back in the 1950s when Flint's text was written, there were some disputes among Scandinavian varve chronologists concerning the number of years elapsed since the retreat of the Pleistocene glaciers from various locations, these problems have now been resolved, and very little uncertainty remains in the varve chronology constructed for the last 10,000-12,000 years. Indeed, varve chronologies are now so well established, they are being used to correct radiocarbon dates for the period 10,000-12,000 yr B.P., just as dendrochronology (tree ring dating) has been used to correct radiocarbon dates for the period 2000-7000 yr B.P.! 
All doubt as to the annual nature of at least the Swedish varves has recently been dispelled by work done by Ingemar Cato,  of the Swedish Geological Survey. Cato has studied varves forming at the present time in the estuary of the Ångermanälven river in northern Sweden. He has proved by direct observation that varves do indeed form as annual deposits and that their thickness is directly related to the amount of material carried in suspension by the river. Now that we know for certain that the Swedish varves are indeed yearly records of the postglacial world, creationists have to decide what to do with the fact that the varve record at Döviken in Sweden began in 7288 BCE (i.e., 4940 years before the date implied by the Bible for Noah's flood). This means that the biblical chronologies spanning the period from the flood to the supposed birth of Christ are in error by more than 310%! This is very hard to reconcile with biblical inerrancy.
Worse yet, the beginning of the varve-count does not signal the end of Noah's flood (of course!), but rather the end of the Ice Age (Pleistocene Epoch) - which epoch most creationists claim is also post-flood. Allowing sufficient time for numerous advances and retreats of continental glaciers, with deep weathering of soils and growth of long-lived forests in between, we see that the date of Noah's flood is pushed back to far before 10,000 BCE, i.e., to long before the beginning of the universe according to the opinion of creationist savants!
The Green River Shale: A Rock That Killed God
While ICR creationists probably get a headache from the contemplation of postglacial varves, the problems presented by preglacial varves ought to squeeze their brains out their hair follicles. Quite a few creationists claim that all the preglacial sedimentary rocks of the world were laid down during the single year of Noah's flood. This would seem to be preposterous enough to make anybody laugh creationism off the stage; but the absurdity grows even greater when one considers the problem creationists face when they have to account for preglacial varved deposits such as the Eocene Green River Shale, a rock deposit found in Colorado, Utah, and Wyoming.
The Green River Shale is a deposit of soft rocks (including so-called oil-shales) averaging about 2000 feet in thickness and covering an area of 25,000 square miles. A large part of the formation consists of laminated deposits that appear to be varves - apparently over six million of them! The first detailed description of the varved deposits was published back in 1929 by Wilmot H. Bradley, a geologist with the U.S. Geological Survey. 
Unlike most modern varved deposits, the Green River varves are very thin, averaging only 0.18 millimeters. In each pair of laminations, one layer is darker in color and much richer in organic material than the other, which often is made of very fine-grained carbonate minerals. Bradley concluded that the varves were annual deposits on the basis of their close resemblance to varves being formed today in certain modern lakes and on the basis of the astronomical rhythms they appear to reflect:
Three cycles of greater length than the varve cycle are suggested by fairly regular recurrent variations in the thickness of the varves and in the thickness and character of certain beds and by the fairly regular spacing of certain salt-mold layers. The first of these cycles averaged a little less than 12 years in length and appears to correspond to the cycle of sunspot numbers. The second cycle had an average length of about 21,600 years and suggests the average period of about 21,000 years which is the resultant of the cyclic changes of eccentricity of the earth's orbit and the cycle of the precession of the equinoxes. The third cycle, which was about 50 years long, agrees with no well-established rhythm. How does Henry Morris deal with this evidence? The presence of astronomical rhythms in the shale being the most impressive argument for a generally annual character of the laminations, we are not surprised to find that Morris makes no mention of the evidence and thus avoids the embarrassment of having to explain it away. Instead, he attacks Bradley's use of the principle of uniformitarianism in comparing the Green River Varves with the annual deposits being formed in certain modern lakes, and he attacks Bradley's calculations showing that the amount of material composing each varve was consistent with the amount of material that could be brought into the lake each year by rivers.
Nowhere does Morris explain how varves reflecting sun-spot and higher astronomical rhythms could have been laid down during the single year of Noah's Flood. Nowhere does he let his readers know the problem even exists. Although he cites various geological treatises that contain greatly detailed information about the Green River Formation, Most of this is ignored. He mentions
the extensive deposits of volcanic ash mingled with the shales and the almost complete absence of any graded bedding in the oil-rich shales such as would be normally encountered in any lake-bottom sediment. Also, there is evidence of brecciated conditions in many parts of the formation. Not only does Morris not explain why it is implausible to suppose that volcanic ash occasionally fell into the lake in which the varves were forming, he neglects to discuss the impossibility of such ash layers forming if the volcanoes producing them were submerged by the waters of Noah's flood! With respect to the supposed lack of graded bedding,  he not only neglects to discuss the limy sandstones which Bradley reported did display graded bedding, he neglects to mention that his own hypothesis of how the deposit was formed during Noah's flood absolutely requires all the layers to display graded bedding!
The only certain conclusion, from the very nature of the deposits, would seem to be that they could not have been formed as cyclic varves as claimed. A possible plausible explanation might be in terms of a vast sedimentary basin formed by the gradual uplift of the land surrounding it, in the later stages of the Deluge period. A complex of shallow turbidity currents, carrying the still soft surface sediments and organic slime from the surface of the rising lands would then enter the basin, mingle, and deposit their loads..." Turbidity currents would have the effect of suspending particles of all sizes in the water. Unless magical powers be invoked to prevent it, all the laminations resulting from turbidity flows would show graded bedding, with coarse particles at the bottom, fine ones at the top. How each turbidity flow could be spread out so thinly over thousands of square miles, Morris does not explain. Nor does he deal with the problem that oil and water do not mix, and that if the oily, organic material forming one part of each varve pair had been washed into the lake basin by a turbidity flow the organic material would form large blobs, not microscopically thin, uniform layers perfectly demarcated from the inorganic layers above and below. Still less does Morris explain how six million turbidity flows could have occurred within the space of one year. Nearly 700 basin-wide turbidity flows would have had to occur per hour!  Morris, as we have already seen, mentions that some of the Green River deposits are "brecciated,"  as though that somehow rules out a generally annual nature of the varves. What he does not tell his readers - even though it is certain that he learned the truth while rummaging through the sources he cites - is that the Green River breccias resulted from mud-flats drying out, with the formation of mud-cracks and the curling up of the resulting algal slime-covered mud shingles. Understandably, Morris did not want to draw attention to evidences of drought at a time he claims the world was under water! Nevertheless, his method here can hardly be confused with honest scholarship.
One Week in Wyoming
Given the information available concerning the types of things found in the Green River Formation, it is amusing to attempt a reconstruction of what Yahweh would have had to do to form it during the single year postulated for Noah's flood.
Since there are over six million two-ply layers, it is clear that our earth-destroying deity had to lay down algae, deposit carbonate, lay down algae, etc., more than six million times! Since the Green River Formation comes rather late in the geological column, it is clear that it would have been formed during the last days of the flood year. If all 600 million years-worth of Phanerozoic rocks were actually formed in about a year, as creation "scientists" claim, formation of the six million laminations of Green River rocks should have taken about a week. Whatever Yahweh was doing that week in Wyoming, he was doing it a rate of about 600 paired layers per minute! Perhaps he had the help of Speedy Gonzalez.
Probably the greatest problem the "Rock of Ages" had in giving the false appearance of age to the Green River Shale stemmed from the fact that he had to do it in the midst of a world-destroying flood, yet many of the structures of the deposit can only be formed during drought. For example, there are many hundreds of layers of salt crystals. This means that at least once per hour, Yahweh had to stop rearranging continents, fly to Wyoming, evaporate the flood waters in just that locality to crystallize and precipitate out layers of salt - without adding heat to destroy the aquatic forms of life he would need to help him form other structures to be discussed later.
Since volcanic ash layers are common in our shale deposit, at least several time per day our rock-making divinity had to pull back the waters enough to let the peaks of the local volcanoes emerge, eject ash clouds, and let the ash settle upon the varves. Then he had to let the flood waters return (waters five miles deep, if Mt. Everest was covered!), until the next drought was needed.
Several times per hour, Jehovah had to remove the water completely from the Green River area, so he could form mud-cracks, coat the mud with a varnish-like layer of algal remains, add dead fish, dry the whole affair until mud shingles and fish alike curled up. Then, unlike his trick with Moses in the Red Sea, he had to let the flood return gently, so that the mud-curls and curled fish would not be disturbed, but would be covered by a delicate cover of varved material. At least once per day, however, Yahweh Elohim had to keep the mud-flats dry long enough for plants to grow and a weathered soil horizon to form.
Despite the fact that the purpose of Noah's flood was to destroy all life on earth, aside from the token delegations taken onto the ark, the Lord God of Sabaoth had to keep lots of living things held at the ready so he could use them to form particular deposits. For example, at least once per day he had to form algal reefs as much as six feet thick, in which live algae were caused to secrete layers of carbonate having the appearance of annual growth rings. Although he probably had less than a minute to do it, the Little Old Rock-Maker managed to form algal reefs looking for all the world as though they had taken at least 350 years to grow!
Periodically, insect larvae by the billions had to be trotted out to cast their exoskeletons in crowded layers between the varves. At other times, the deity took just the eyes and wing-scales of insects and made rock layers from them. Sometimes, for variety, he made layers out of the scales of ganoid fishes instead of the scales of insects. (Most of the organic layers, of course, are made up of the spores of algae and fungi and the amorphous remains of other vegetation.) Occasionally, he drowned a camel or sank a crocodile, and laid it out upon the varved clays. Just where these animals had been treading water during the preceding ten months of the flood is not revealed in Genesis, although the prophets at ICR could get a special revelation on the subject at any time.
Of all the marvelous portions of the Green Rive Shale, the ones that most vividly display divine design are, without question, the layers formed mostly of tiny coprolites - the fossilized excremental pellets of aquatic insects and other tiny water-dwelling animals. It is awesome to contemplate a being who repeatedly would take time off from the important job of destroying the world, in order to call out the trillions of tiny insects and crustaceans that he had been saving from destruction - just for the purpose of having them all poop on the playa en masse. Who but a god could make all those little buggers "hold it" until that one-tenth of a second when their colon contents were needed to form a particular varve?