Notre Dame at Paris, in particular, is a curious example of this variety. Every face, every stone of the venerable monument is a page not only of the history of the country, but also of the history of science and art. Thus, to allude only to leading details, while the little Porte Rouge attains the almost extreme limit of the Gothic refinement of the fifteenth century, the pillars of the nave, in their size and gravity of style, go back to the Carlovingian Abbey of Saint-Germain des Prés. One would say that there was an interval of six centuries between that door and those pillars. Even the Hermetics find among the symbols of the great door a satisfactory epitome of their science, of which the Church of St. Jacques de la Boucherie formed so complete a hieroglyph. Thus, the Roman abbey, the philosopher's church, Gothic art, Saxon art, the clumsy round pillar, which recalls Gregory VII., the hermetic symbolism by which Nicholas Flamel paved the way for Luther, papal unity, schism, Saint-Germain des Prés, Saint-Jacques de la Boucherie, are all confounded, combined and blended in Notre Dame. This central and generative church is a kind of chimera among the old churches of Paris; it has the head of one, the limbs of another, the trunk of a third, something of all. Considering here Christian European architecture only, that younger sister of the grand piles of the Orient, we may say that it strikes the eye as a vast formation divided into three very distinct zones or layers, one resting upon the other; the Roman zone, (the same which is also known according to place, climate, and species, as Lombard, Saxon, and Byzantine. There are the four sister forms of architecture, each having its peculiar character, but all springing from the same principle, the semicircular arch,) the Gothic zone, the zone of the Renaissance, which may be called the Greco-Roman. The Roman stratum, which is the oldest and the lowest, is occupied by the semicircular arch, which reappears, together with the Greek column, in the modern and uppermost stratum of the Renaissance. The painted arch is between the two. The buildings belonging to any one of these three strata are perfectly distinct, uniform, and complete. Such are the Abbey of Jumieges, the Cathedral of Rheims, the Church of the Holy Cross at Orleans. But the three zones are blended and mingled at the edges, like the colors in the solar spectrum.