trace out the various modes in which, during the ages of the past, Nature has wrought out the same leading plan, sounding, as it were, an ever-changing series of modulations upon one key-note. In comparing together the ganoids of the Old Red Sandstone and the Carboniferous rocks, he finds that in the asterolepis--a fish belonging to the lower part of the former formation--the pointed arch formed by the sweep of the lower jaws is filled up by a single plate like some abbey-window with its mullions knocked away, and built up with rude stone and lime. Higher in the same group of rocks he meets with the cranium of the holoptychius, where there is one straight central mullion running in an unbroken line from the angle of the arch to its base. In the osteolepis[43] he sees this mullion branching into two at its upper end, so that the window consists of three divisions, as in the simplest style of Gothic. Passing upwards into the Carboniferous system, he encounters a still more ornate arrangement in the cranium of the megalichthys. The central mullion with its two upper branches still remains, but it is flanked by an additional one on each side, from which there spring six cross bars that diverge obliquely with a slight curve, so as to join the outer arch and subdivide the window into nineteen compartments. So varied are the plans of the Divine Architect in what to man may seem such a little matter as the piecing together of a fish's skull. [Footnote 43: Hugh Miller's _Footprints of the Creator_, p. 91.]