Geology is a science in which accidental exceptions are likely to occur. Only when we find strata in their original relative positions can we surely infer that the order of succession is the order of time. But it not uncommonly happens that strata are inverted by the bending and doubling action of extreme pressure. Landslips may carry one body of rock into proximity with an unrelated series, and produce results apparently inexplicable.12 Floods, streams, icebergs, and other casual agents, may lodge remains in places where they would be wholly unexpected. Though such interfering causes have been sometimes wrongly supposed to explain important discoveries, the geologist must bear the possibility of interference in mind. Scarcely more than a century ago it was held that fossils were accidental productions of nature, mere forms into which minerals had been shaped by no peculiar cause. Voltaire appears not to have accepted such an explanation; but fearing that the occurrence of fossil fishes on the Alps would support the Mosaic account of the deluge, he did not hesitate to attribute them to the remains of fishes accidentally brought there by pilgrims. In archæological investigations the greatest caution is requisite in allowing for secondary burials in ancient tombs and tumuli, for imitations, forgeries, casual coincidences, disturbance by subsequent races or by other archæologists. In common life extraordinary events will happen from time to time, as when a shepherdess in France was astonished at an iron chain falling out of the sky close to her, the fact being that Gay-Lussac had thrown it out of his balloon, which was passing over her head at the time.
Novel and Unexplained Exceptions.
When a law of nature appears to fail because some other law has interfered with its action, two cases may present themselves;—the interfering law may be a known one, or it may have been previously undetected. In the first case, which we have sufficiently considered in the preceding section, we have nothing to do but calculate as exactly as possible the amount of interference, and make allowance for it; the apparent failure of the law under examination should then disappear. But in the second case the results may