His faith in the uniformity of nature (except man's mind) was set out in a theological argument; if God is a lawgiver, then a "miracle" would break the lawful edicts that had been issued at Creation. Therefore, a belief in miracles would be entirely atheistic. Powell's most significant works defended, in succession, the uniformitarian geology set out by Charles Lyell and the evolutionary ideas in "Vestiges of the Natural History of Creation" published anonymously by Robert Chambers which applied uniform laws to the history of life in contrast to more respectable ideas such as catastrophism involving a series of divine creations. "He insisted that no tortured interpretation of Genesis would ever suffice; we had to let go of the Days of Creation and base Christianity on the moral laws of the New Testament."