A superior addition to the National Mall. The bulges and flexes of this building's honey-colored limestone walls evoke wind-sheared Western mesas. Inside and out there are passages good enough to bear comparison to the suavely rippling walls of Alvar Aalto, the great Finnish apostle of forms derived from nature. For the most part this is the work of Douglas Cardinal, architect of the lyrical swells of the Canadian Museum of Civilization near Ottawa. It was Cardinal, a Blackfoot Indian, who won the original commission in 1993 to design the museum in affiliation with other architects. Because of a dispute with the museum's directors over deadlines, a team of outside architects was later brought in to finish the project. Cardinal has dissed the details of the completed building, but the broad outlines are unmistakably his. And the broad outlines are quite something.