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Rh fact that while the bedding in Xormandy is level, that at Carrara is steep, and that the forces which raised the beds of Carrara crystallized them also, so that the cleavage which is all-important in the stones of my garden wall is of none in the duomo of Pisa,—simply determined the possibility of the existence of Pisan sculpture at all, and regulated the whole life and genius of Nicholas the Pisan and of Christian art. And, again, the fact that you can put stones in true bedding in a wall, but cannot in an arch, determines the structural transition from classical to Gothic architecture.

154. The structural transition, observe; only a part, and that not altogether a coincident part, of the moral transition. Read carefully, if you have time, the articles 'Pierre' and 'Meneau' in M. Viollet le Duc's Dictionary of Architecture, and you will know everything that is of importance in the changes dependent on the mere qualities of matter. I must, however, try to set in your view also the relative acting qualities of mind.

You will find that M. Viollet le Duc traces all the forms of Gothic tracery to the geometrical and practically serviceable development of the stone 'chassis,' chasing, or frame, for the glass.