the lighter parts of the crust; and there seems to be little doubt that both of these principles have been employed in constructing the "pillars which support the earth." It is evident, however, that an arch thrown over the internal abyss of the earth, or a portion of its crust so lightened as to be pressed upward by its heavier surroundings, must, when once established, have become a permanent feature of the earth's foundations, not to be disturbed without calamitous consequences to its inhabitants. [151] Transactions Royal Society of Canada, 1892. It is the part of the philosophical naturalist to bring together these apparent contrarieties of mutation and permanence; both of which are included, each in its proper place, in the great plan of nature. It is therefore my purpose in the present chapter to direct attention to some of the terminal points or fixed arrangements that we meet with in the course of the geological history, and even in its earlier parts, and more particularly in reference to the organic world. This, which is in itself constantly changing, has been placed under necessity to adhere to certain determinations fixed of old, and which regulate its forms and possibilities down to our own time. The argument, as we have seen in a previous chapter, for the animal nature of Eozoon depends on our assuming certain parts of this fixity. We suppose that then as now calcium carbonate had been selected as the material for the skeletons of such creatures; that then, as now, minute tubuli and large canals were necessary to enable the soft animal matter to permeate and pass through the skeleton, and that the protoplasmic animal matter of these far back geological periods had the same vital properties of contraction and extension, digestion, etc., that it has to-day. Could any one prove that these determinations of vital and other forces had not been established, or that living protoplasmic matter, with all its wonderful properties, had not been constructed in the Laurentian period, the existence of this ancient animal would be impossible. Yet how much is implied in all this, and though nothing is more unstable chemically or vitally than protoplasm, if it were introduced in the Laurentian, it has continued practically unchanged up to the present time. If we pass on to the undoubted and varied life of the Cambrian period, we shall find that multitudes of things which might have been otherwise were already settled in a way that has required no change.