Free Hen’s Teeth and Horse’s Toes by Stephen Jay Gould Page B

seventeenth-century texts. It mattered little that the insane did not work for biological or psychological reasons, and the unemployed for want of opportunity.
    Steno also reordered the world in a way that must have seemed as curious to his contemporaries as the amalgamation of madness and poverty seems to us. As his contemporaries gathered the idle, Steno identified solids within solids as a fundamental class of objects, divided them from everything else, and developed a set of criteria to sort his solids into subdivisions representing the different causes that fashioned them. The great Prodromus is, fundamentally, a treatise on a new system of classification for solids within solids—a classification by common genesis, rather than superficial similarity of outward appearance. Steno’s revolution in thought arises from his altered classification—and his curious title, so understood, could not be more devastatingly appropriate. I have read the Prodromus many times, but when I finally understood its message, just last month, that bizarre title sent a shiver up my spine.
    The Prodromus has usually been misinterpreted by geologists who attribute Steno’s success to his use of modern observational methods. (In fact, although the Prodromus is sprinkled with astute observations, its longest section is a speculative discussion on the origin of solid bodies, based on the incorrect premise that all solids must be generated from liquids, and that the form of a solid indicates the motions of the liquids that produced it.) His translator writes, for example: “At a time when fantastic metaphysics were rife, Steno trusted only to induction based upon experiment and observation.” But the Prodromus reports no real experiments and only a modest number of observations. It succeeded primarily because Steno followed a metaphysic congenial with our own, but relatively new in his time.
    Geologists have also judged Steno inappropriately by searching the text for gems of “modern” insight, rather than by understanding its argument as a totality. Thus, the commonest statement about the Prodromus , often the only statement made by geologists, holds that Steno presented the crystallographic law of the constancy of interfacial angles—that however much the size and shape of crystal faces vary, the angles between them remain the same. Well, perhaps he did, but the “law” appears as two throwaway lines in a figure caption, and has little relation to Steno’s major theme or argument. (It arises simply as a corollary to his speculations about inferring the motion of fluids from the form of solids precipitated from them.)
    No, the Prodromus is, as its title states, about solids in solids and their proper classification by mode of origin. It is founded upon two great taxonomic insights: first, the basic recognition of solids within solids as a coherent category for study and, second, the establishment of subdivisions to arrange solids within solids according to the causes that fashioned them.
    Steno uses two criteria for his subdivisions. (They are blessedly obvious once you state the problem, but Steno’s revolution is the statement itself.) First, in what might be called the principle of molding, Steno argues that when one solid lies within another, we can tell which hardened first by noting the impress of one object upon the other. Thus, fossil shells were solid before the strata that entomb them because shells press their form into surrounding sediments just as we make footprints in wet sand. But surrounding rocks were solid before the calcite veins that run through them because the calcite fills preexisting channelways just as Jello matches the flutes of a mold. The principle of molding allows us to establish the temporal order of formation for two objects in contact. In a world still regarded by many of Steno’s contemporaries as formed all at once by divine fiat, this criterion of history struck a jarring chord and eventually forced a