"Countless millions of foraminifera inhabit the waters of the North Atlantic (and of other deep seas) at the present day; and of these at least one species—Globigerina bulloides—cannot be distinguished from one of the commonest species found in the White Chalk. When these tiny animals die their soft parts soon decay and disappear, and their skeletons (or shells) fall on the sea floor, where they form a whitish mud or 'ooze.' The time required for the accumulation of so thick a deposit composed of the remains of organised beings—the White Chalk is in Norfolk quite 1200 feet thick—must have been very great. If we allow that the tiny shells of the foraminifera may have accumulated at the rate of two feet in thickness in a century, then it would have required 50,000 years to form the chalk of the south-east of England, whose thickness we have estimated at 1000 feet."
Every one who has been on a chalk cliff or hill has found, and perhaps thrown, chalk flints. Flints are made of mineral called silica, and very often these flints, or nodules of silica, surround some organism like a sponge or a shell. During the formation of the chalk the sea floor appears to have been covered at intervals by a growth of sponges, which were composed of siliceous matter, and their death and decay produced most of the flint. Sometimes flint is found in bands, in which case it may have been deposited by siliceous water trickling through fissures or cracks in the chalk.
In the sea which thus existed the Plesiosaurs and Ichthyosaurs still pursued the even tenor of their way, growing larger and larger. They were of many shapes, and probably of many habits. Some were certainly fish-eaters, and with their enormous jaws must have been most undesirable neighbours. Probably, however, they had plenty of diversity in their lives, and may have had many a bitter struggle with equally ferocious sea animals of other types. The scaly saurians, for example, were beginning to come on; and began in this era to assume the size and appearance that have occasionally since been attributed to sea serpents. These reptiles, known as Dolichosaurs, were long-necked, lizard-like reptiles in the beginning of their career, and grew longer and longer in succeeding generations, till at last their descendants were so long and snaky that geologists have called the later specimens "serpents." These sea serpents were from fifteen to forty-five feet in length, and their remains have been found in the valley of the Meuse. They do not seem to have had a very long career, for they do not appear after the Chalk Age, and no direct descendants are known; but while they lived they ranged from North and South America to Europe and New Zealand.
The first true sea turtles appeared and lived and extended their families in great variety. They had broad flat forms, their shells only just covering their ribs like a short Eton jacket; but they were very large. The greatest of them, Archelon, had a skull larger than that of a horse, and must have measured fully twelve feet across the shell.
We may consider the birds at the same time as the sea animals or sea reptiles, since they, perhaps, were relations. Moreover, while the birds of Jurassic times were land birds, those of the Chalk period were aquatic. These birds belonged to two widely different classes, one consisting of large birds which did not fly, the other of small birds with great strength of wing and great powers of flight. Of the first kind was the Hesperornis. This was a large flightless bird, specially adapted to diving. Its wings hardly existed, for they had only one bone left; and that implies the passage of a very long flight of time, during which the wings once in existence had become more and more useless, till they had dwindled to a mere nothing. But the Hesperornis had enormously strong legs, which were used as paddles, and their efficiency was increased by the bones of the foot being so joined to the leg as to turn edgewise in the water when brought forward. Any one who has ever paddled a Canadian canoe will appreciate the advantage of this. But this was not all, for the legs were so joined to the body-frame as to stand out nearly at right angles (like a pair of oars), instead of standing under the body as walking legs do. Apparently walking as well as flying had been abandoned, and this bird had become a diver and swimmer merely. The head, neck, and body were long, and admirably shaped for plunging through the water. Favoured by the powerful hind limbs, the Hesperornis must have been very swift both on and under the water, and a formidable enemy to the fishes on which it preferred to feed. Its jaws were armed with teeth set in a groove, and, like the jaws of snakes, were separable so as to admit large prey. As these strange birds were sometimes six feet long, they must have been able to account for fish and reptiles of considerable size. They probably lived nearly altogether on and in the water.
The second type of bird, Ichthyornis, were small birds, scarcely larger than pigeons and a little like terns in appearance. They were splendid fliers, and were armed with teeth set in sockets. Their legs and feet were small and slender, but their wings very strongly developed. They frequented the same seas and places as the Hesperornis, and yet the two were farther apart in structure than any two types of birds now living. Compared with the Archæopteryx, both these types of birds show progress in the shortening of the long, curiously feathered tail and the loss of the fingers and claws; but both retained the teeth of primitive birds. We may perhaps be allowed to depart from the strict adherence to geologic chronology by tracing here, instead of in the next chapter, the subsequent history of the early birds. In the strata of the next era remains of various birds were found. One of great interest, on account of its enormous size, was the Pharorachus of America. It was rather like, in type, a living bird known as the Cariama or Screamer. But if the extinct bird (of which the skull only has been found) had the general proportions and habits of the Cariama it must have been a terrible monster, standing some twelve feet high, and far exceeding the most powerful eagles and vultures in strength and the size of its beak and claws. Great extinct wingless birds are found in the quite recent "alluvial" deposits in New Zealand and Madagascar.
Something more than half a century ago a piece of bone was sent to Sir Richard Owen by a visitor to New Zealand who had just arrived there, and who had found it in his garden. Professor Owen, on examination, was able to say, from the general make and structure of the bone, that it was the bone of a bird. It was about seven or eight inches long. On examining the ridges and various marks on the bones, Owen was able to say that it was identical with the middle of the thigh-bone of an ostrich. He ventured then to publish that this bone was a proof that there existed formerly in New Zealand a huge land bird like the ostrich, only bigger. After a few years more bones were sent to Owen from New Zealand, which entirely confirmed what he said; and in the course of a few years he was able to put together from the bones sent a skeleton with enormous legs and neck—the skeleton of the ostrich-like bird the Moa of New Zealand. Since that time a great number of these birds have been found buried in the morasses and swamps of that country. The Moa is allied to the ostriches of Africa, the emus and cassowaries of Australia, and the rheas of South America.
The Moa of Madagascar was smaller, and is known as the Æpyornis. But it lays the largest egg known, a tremendous thing as big as a Rugby football. It was this very large egg which inflamed the imagination of ancient navigators, and led to the vast exaggeration in describing the so-called "Roc," which Sindbad met with in the Arabian Nights. In concluding these brief notes on extinct birds we must also mention the present-day "kiwi" in New Zealand, which resembles in some respects the Apteryx, or most ancient of birds.
Let us now return to the land reptiles of the Chalk period. These are chiefly found in America, which was not submerged, as the greater part of Europe was, beneath the ocean. The incursion of the sea was more limited in the western hemisphere, and the land area was large enough to allow the continued progress of the land reptiles, though even here the sea reptiles seem to have done best. The great Dinosaurs still kept in the forefront, but they were not quite so pre-eminent as heretofore. The flesh-eating forms were less abundant, though among them an enormous kangaroo-like reptile, fifteen feet long, made its appearance. The Dryptosaurus must have been speedy, very powerful, and its habits must have made it appear like an ogre in seven-league boots to its smaller inoffensive neighbours. The Spoonbill Dinosaurs (Hadrosaurus) were very curious creatures, who also faintly resembled a kangaroo, but had enormous lower parts and crocodile-like tails.
But the most singular development appeared in the Ceratops family of the vegetarian reptiles, particularly in the genus called Triceratops. These were very large quadrupeds with enormous skulls which stretched back over the neck and shoulders in an enormous cape or hood of bone. Added to this was a sharp parrot-like beak, a stout horn on the nose, a pair of large pointed horns on the top of the head, and a row of projections round the edge of the cape. The Triceratops wanted all the protection it could get, for it had no intelligence worth mentioning. Professor Marsh remarks that they had the largest heads and the smallest brains of the reptile race.