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.

Hence, we have certain complex structures, buildings of gradation and
transition, which may be Roman at the base, Gothic in the middle, and
Greco-Roman at the top. This is caused by the fact that it took six
hundred years to build such a fabric. This variety is rare. The donjon-
keep at Etampes is a specimen. But monuments of two formations are more
frequent. Such is Notre-Dame at Paris, a structure of the pointed arch,
its earliest columns leading directly to that Roman zone, of which the
portals of Saint-Denis and the nave of Saint-Germain des Pres are perfect
specimens. Such is the charming semi-Gothic chapter-house of Boucherville,
where the Roman layer reaches midway. Such is the cathedral of Rouen,
which would be wholly Gothic if the tip of its central spire did not dip
into the zone of the Renaissance. [Footnote: This part of the spire, which
was of timber, happens to be the very part which was burned by lightning
in 1823.]

However, all these gradations and differences affect the surface only of
an edifice. Art has but changed its skin. The construction itself of the
Christian church is not affected by them. The interior arrangement, the
logical order of the parts, is still the same. Whatever may be the carved
and nicely-wrought exterior of a cathedral, we always find beneath it, if