XII. And, in order to avoid an over use of this liberty, it would be well to consider what application may be conveniently made of the dovetailing and various adjusting of stones; for when any artifice is necessary to help the mortar, certainly this ought to come before the use of metal, for it is both safer and more honest. I cannot see that any objection can be made to the fitting of the stones in any shapes the architect pleases: for although it would not be desirable to see buildings put together like Chinese puzzles, there must always be a check upon such an abuse of the practice in its difficulty; nor is it necessary that it should be always exhibited, so that it be understood by the spectator as an admitted help, and that no principal stones are introduced in positions apparently impossible for them to retain, although a riddle here and there, in unimportant features, may sometimes serve to draw the eye to the masonry, and make it interesting, as well as to give a delightful sense of a kind of necromantic power in the architect. There is a pretty one in the lintel of the lateral door of the cathedral of Prato (Plate IV. fig. 4.); where the maintenance of the visibly separate stones, alternate marble and serpentine, cannot be understood until their cross-cutting is seen below. Each block is, of course, of the form given in fig. 5. XIII. Lastly, before leaving the subject of structural deceits, I would remind the architect who thinks that I am unnecessarily and narrowly limiting his resources or his art, that the highest greatness and the highest wisdom are shown, the first by a noble submission to, the second by a thoughtful providence for, certain voluntarily admitted restraints. Nothing is more evident than this, in that supreme government which is the example, as it is the centre, of all others. The Divine Wisdom is, and can be, shown to us only in its meeting and contending with the difficulties which are voluntarily, and _for the sake of that contest_, admitted by the Divine Omnipotence: and these difficulties, observe, occur in the form of natural laws or ordinances, which might, at many times and in countless ways, be infringed with apparent advantage, but which are never infringed, whatever costly arrangements or adaptations their observance may necessitate for the accomplishment of given purposes. The example most apposite to our present subject is the structure of the bones of animals. No reason can be given, I believe, why the system of the higher animals should not have been made capable, as that of the _Infusoria_ is, of secreting flint, instead of phosphate of lime, or more naturally still, carbon; so framing the bones of adamant at once. The elephant or rhinoceros, had the earthy part of their bones been made of diamond, might have been as agile and light as grasshoppers, and other animals might have been framed far more magnificently colossal than any that walk the earth. In other worlds we