Certainly not one of the higher animals was of the same species as any of those now in existence.  The beasts of the field, in the days before the chalk, were not our beasts of the field, nor the fowls of the air such as those which the eye of men has seen flying, unless his antiquity dates infinitely further back than we at present surmise.  If we could be carried back into those times, we should be as one suddenly set down in Australia before it was colonized.  We should see mammals, birds, reptiles, fishes, insects, snails, and the like, clearly recognizable as such, and yet not one of them would be just the same as those with which we are familiar, and many would be extremely different.

From that time to the present, the population of the world has undergone slow and gradual, but incessant, changes.  There has been no grand catastrophe—­no destroyer has swept away the forms of life of one period, and replaced them by a totally new creation:  but one species has vanished and another has taken its place; creatures of one type of structure have diminished, those of another have increased, as time has passed on.  And thus, while the differences between the living creatures of the time before the chalk and those of the present day appear startling, if placed side by side, we are led from one to the other by the most gradual progress, if we follow the course of Nature through the whole series of those relics of her operations which she has left behind.  It is by the population of the chalk sea that the ancient and the modern inhabitants of the world are most completely connected.  The groups which are dying out flourish, side by side, with the groups which are now the dominant forms of life.  Thus the chalk contains remains of those strange flying and swimming reptiles, the pterodactyl, the ichthyosaurus, and the plesiosaurus, which are found in no later deposits, but abounded in preceding ages.  The chambered shells called ammonites and belemnites, which are so characteristic of the period preceding the cretaceous, in like manner die with it.

But, amongst these fading remainders of a previous state of things, are some very modern forms of life, looking like Yankee pedlars among a tribe of Red Indians.  Crocodiles of modern type appear; bony fishes, many of them very similar to existing species, almost supplant the forms of fish which predominate in more ancient seas; and many kinds of living shell-fish first become known to us in the chalk.  The vegetation acquires a modern aspect.  A few living animals are not even distinguishable as species, from those which existed at that remote epoch.  The Globigerina of the present day, for example, is not different specifically from that of the chalk; and the same maybe said of many other Foraminifera.  I think it probable that critical and unprejudiced examination will show that more than one species of much higher animals have had a similar longevity; but the only example which I can at present give confidently is the snake’s-head lampshell (Terebratulina caput serpentis), which lives in our English seas and abounded (as Terebratulina striata of authors) in the chalk.