museums often developed purely formalistic artifact classifications based on criteria of size, shape, and color alone (e.g., Rau 1876). When using this procedure, groups of similar-appearing artifacts were displayed together without any consideration for their times or places of origin. This tradition persisted in the display of many kinds of museum materials until well into the twentieth century.

General a. h. pitt rivers, often regarded as the father of scientific archaeology in Great Britain, went beyond other museum curators in combining classificatory formalism with evolutionism. So committed was he to a unilinear evolutionary perspective that he arranged all of the objects in his vast collection—both ethnographic and archaeological—into what he believed to be developmental sequences without any reference to their place of origin (Pitt Rivers 1874). Pitt Rivers may thus have been the first prehistorian to employ purely logical seriation, although the technique had certainly been used earlier by art historians. Combined with more formal typology, it would later by used by scholars like sir william matthew flinders petrie and Alfred L. Kroeber to develop culture sequences in areas where direct chronological evidence was lacking. That is, types were initially defined on formal grounds and then arranged into what appeared to be logical developmental sequences.

The single most important revolution in artifact classification came about as a result of the introduction of frequency seriation in the early decades of the twentieth century. This procedure grew out of a recognition that cultures generally change gradually rather than cladistically. At any given time, some types of artifacts are always coming into use while others are going out. After the passage of a generation or two all of the same artifact types may still be in use as at the beginning, but some will have increased in frequency while others will have decreased. Accordingly, cultures and their various developmental phases need not always be recognized by diagnostic artifact types or assemblages; they can also be recognized by diagnostic frequencies of artifacts, even when there are no individually diagnostic types.

The frequency seriation method appears to have been pioneered by two scholars working at nearly the same time in different parts of New Mexico. Excavating in the Tano ruins near the Rio Grande, nels nelson was able to assign the various ruined pueblos to five successive chronological periods on the basis of pottery wares and ware percentages present or absent (Nelson 1916). Before he could make numerical calculations, however, Nelson first had to identify and name all of the different wares present in his collections. At about the same time, AlfredL. Kroeber was collecting potsherds from the surfaces of ruined pueblos in western New Mexico (Kroeber 1917), and without any excavation at all, he was able to suggest a sequence of the ruins based on the frequency or infrequency of particular wares. Once again, this method necessarily involved an initial classification of the wares. Later, Kroeber was to apply the same principles in the classification of pottery collections and of culture horizons in Peru (Kroeber 1944).

Frequency seriation introduced for the first time the procedure of quantification in artifact classification, and this procedure involved two important methodological correlates. First of all, if types were to be treated quantitatively, classifications had to be fully comprehensive; there had to be a type category for every shard or point. Moreover, the categories had to be mutually exclusive. In other words, the classification had to be a true typology. Second, the frequency seriation approach had the effect of partially decoupling artifact classification from culture classification. That is, types might not necessarily be diagnostic of any one period or even of any one culture yet their relative frequency could help in the definition of periods and cultures.

The activities and the success of Nelson and Kroeber inaugurated an era of almost feverish identification and naming of prehistoric pottery types, first in the southwestern United States and before long in neighboring areas as well. Once again, as in the case of culture classification, the proliferation of newly proposed types led to a perceived need for more formal systematics. Here again, the Gladwins took the