[OAB 89] It is well-known to geologists that, when temperatures and pressures are high, rocks will behave like an extremely high-viscosity fluid (kind of like Silly Putty, but even much thicker than that). You may know that, if you hit a piece of Silly Putty with a hammer, it will shatter just as a rock would do. However, you can bend Silly Putty around into shapes if you do it slowly enough, and rocks can do the same thing (although they require the bending to be as slow as many thousands of years, rather than a few seconds as it is for Silly Putty). If sedimentary rocks were buried, so that they were subjected to high temperature and pressure, and then folded by forces of plate tectonics, it is easily shown that folded strata could occur. By the way, the young-Earth claim (which supposes that these were sand layers that were folded before they hardened) cannot explain what force could have folded the layers in such a short time.