The hundredth meridian, or a line drawn north and south near Toluca, divides ancient Mexico into an eastern half, of high civilizations in densely populated regions, and a western half, of scattered, small, and isolated tribal groupings, whose archaeological history has been recovered only in the last twenty years. In the main, this western history comprises four principal stages: (1) an early era of Olmec style which endured many centuries in Guerrero, with sporadic manifestations farther west; (2) a middle period when many traits of a village art in the style of the Formative period were amplified in the funeral pottery of Colima, Jalisco, and Nayarit; (3) post-Classic intrusions of Toltec and Mixtec ceremonial forms in Michoacán and in the pottery of Sinaloa on the north-west coast; and finally, (4) coeval with the state which resulted from the Aztec conquest, the Tarasca civilization centring upon the lake district of Michoacán.1
Save in Guerrero, all these western styles of art were of recent origin, not antedating Teotihuacán III. Another striking peculiarity of the western cultures corresponds to the division by pre-Classic and Classic stages: in Guerrero, only the lithic industries seem to have survived, while in the rest of western Mexico, pottery products carry the record, almost to the exclusion of stone. Thus Guerrero alone has a pre-Classic archaeological history, and Guerrero alone is rich in stone manufactures. In other western regions, the artifacts are of Classic date or later, and predominantly ceramic in character. Guerrero belongs together with Olmec, Maya, and central Mexican art; the regions to the north and the west of it belong to another order of civilization which perpetuated early village art rather than the styles of the great ceremonial centres.
South-west of Mexico City lie Tasco and Iguala, on the highway which crosses an ancient archaeological province. This province centres upon the middle course of the Mezcala river. The mining area of Sultepec marks its north-west boundary; Zumpango del Río and Chilapa define its south-eastern limit. Stone objects in great numbers come from the region without specific provenience, casually or illegally excavated and marketed.2 One class is of Olmec style; another reflects Teotihuacán influence in the area; still another group of small face panels of stone is related to post-Classic funeral customs.
A fourth group contains hand-axes, carved to resemble standing human figures looking like insects. This raises a crucial question concerning the origins of stone sculpture.3 To present knowledge, the Olmec style is the oldest dated style of stonework in Mexico. As suggested earlier (p. 66), the Olmec instrumental forms, such as hand-axes,