''I am quite convinced that all religions, at bottom, are pretty much alike. On the surface they may seem to differ greatly, but what appears on the surface is not always religion. Go beneath it, and one finds invariably the same sense of helplessness before the cosmic mysteries, and the same pathetic attempt to resolve it by appealing to higher powers.''--from Treatise on the GodsH. L. Mencken is perhaps best known for his scathing political satire. But politicians, as far as Mencken was concerned, had no monopoly on self-righteous chest-thumping, deceit, and thievery. He also found religion to be an adversary worthy of his attention and, in Treatise on the Gods, he offers some of his best shots, a choreographed cannonade.Mencken examines religion everywhere, from India to Peru, from the myths of Egypt to the traditional beliefs of America's Bible Belt. He compares Incas and Greeks, examines doctrines, dogmas, sacred texts, heresies, and ceremonies. He ranges far and wide, but returns at last to the subject that most provokes him: Christianity. He reviews the history of the Church and its founders. ''It is Tertullian who is credited with the motto, Credo, quia absurdum est: I believe because it is incredible. Needless to say, he began life as a lawyer.'' Mencken is no less interested in the dissidents: ''The Reformers were men of courage, but not many of them were intelligent.'' Against the old-time religion of fellow countrymen, Mencken posed as a figure of old-time skepticism, and he reaped the whirlwind. Controversial even before it was published in 1930, Treatise on the Gods remains what its author wished it to be: the plain, clear challenge of honest doubt.