The decided prevalence of curved forms is worthy of remark. With all their fertility of invention, the inhabitants of this valley seem never to have achieved the rectangular linked meander, or anything more nearly approaching it than the current scroll or the angular guilloche, while other peoples, such as the Pueblos of the Southwest and the ancient nations of Mexico and Peru found in it a chief resource. The reasons for this, as well as for other peculiarities of the decorative art of the mound-builders as embodied in pottery, must be sought for in the antecedent and coëxistent arts of these tribes. These peoples were certainly not highly accomplished in the textile arts, nor had they felt the influence of advanced architecture such as that of Mexico. The influence of such arts inevitably gives rise to angular geometric figures. Taken as a whole, the remains of the mound-builders would seem to point to a hyperborean origin for both the people and their arts. The origin of decorative ideas, the processes by which they are acquired by the various arts, and their subsequent mutations of form and significance are matters of the greatest interest, and a separate paper will be devoted to their consideration. CLASSIFICATION OF FORMS.--Form cannot be made a satisfactory basis of classification, yet within a given group of products, defined by general characters, a classification by shape will be found to facilitate description. In making such a classification we must distinguish essential from non-essential features, that is to say, for example, that bowls must be placed with bowls, bottles with bottles, etc., disregarding the various fanciful modifications given to rims, necks, and bodies for the sake of embellishment. To recognize these adventitious features, which are almost infinite in variety, would be to greatly embarrass form classification. There is also another difficulty in the employment of form in classification--the nomenclature is very imperfect. We cannot use Greek names, as our forms correspond in a very few instances only with the highly developed forms known to classic art. Our own plain terms, although defective, are better and far more appropriate. All necessary correlations of form can readily be made when the comparative study of the pottery of the world is undertaken. If we take a full set of these primitive vessels and arrange them in the order of increasing complexity we have an unbroken series ranging from the simplest cup to the high-necked bottle with perforated foot or with tripod. A partial series is shown in the upper line, Fig 361. A multitude of variations from these outlines are found, a few of which are suggested in the lower line. [Illustration: FIG. 361.--Scale of forms.] Compound, eccentric, and life forms are given elsewhere.