CREATION BY EVOLUTION
slate of Lower Cambrian age, the most marvellous impressions of delicate and fragile organisms have been found—mere films of carbon against the slate—with all their detail of structure preserved with the utmost fidelity. These impressions show many of the relatively high invertebrate types, such as worms, crustaceans, and echinoderms, and here there might well be preserved the ancestral stock out of which the backboned creatures arose, although, so far as actual discovery goes, that record is much later in time.
Except for a persistent type of being variously known as Amphioxus or Branchiostoma, which to this day inhabits the shallow waters bordering the continents, there is again no trace of the important link connecting the vertebrates with their invertebrate forebears. To those of us who are prehistorically interested this is perhaps the most coveted of all the missing links, for its discovery will help to settle arguments that have arisen in favor of this or that method of origin, about which so little is really known.
In Silurian time there came the sharks, known largely from their fossil teeth, some so much like the teeth of modern persistent survivors that the external form and habits of life of some of the early species may be safely surmised by analogy, although others are unlike any that now exist. Of their gradual evolution, especially in the favored lines which were to produce the higher fishes, sufficient, perhaps, is known. Out of one armored group, however, there were to arise the land-living vertebrates. Here again there is more hypothesis than observed fact, and especially desirable would be the discovery of fishes whose fins show potentialities, either in their structure or their implied use, or both, of giving rise to the shore-adapted foot, the point of departure of all terrestrial progression. There is at Yale a single footprint, which speaks volumes to those who read its lesson
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