At the Heart Mountain formation, Wyoming, and at other places, strata are in the wrong order, according to the uniformitarian view, supposedly older rocks being on top of supposedly younger ones. Such formations have been ascribed to the over-thrusting of older rock over the younger. However, at many of these formations, including Heart Mountain, there is no physical evidence for such sliding; nor is there any proof that such motion is mechanically possible. Some recent investigation has again failed to provide any evidence that Heart Mountain was overthrusted; but there is evidence that a normal vertical fault was involved.