The Romance of Modern Geology / Describing in simple but exact language the making of the earth with some account of prehistoric animal life

by Edwin Sharpe Grew

CHAPTER XXI

THE CHALK PERIOD

Once again the European continent and with it Great Britain began to sink. Great Britain at the beginning of the era which followed the Jurassic system, was joined to France, but south of this barrier was a great fresh-water lake, into which rivers and streams poured from the north and the east. Great forests grew on its borders, forests still crowded with ferns and cycads as in previous ages, but affording scope for pine trees to grow as well. On its borders flourished the giant Iguanodon, a great lizard-like animal which could raise itself on its hind legs and lift a fifteen-foot body so as to feed on the branches of the trees. The Iguanodon is a specially interesting fossil reptile, because it was one of the first to be discovered. The first bones and teeth of the Iguanodon were found seventy years ago by a celebrated and most delightful explorer of the earth's crust, Dr. Gideon Mantell, in the strata known as the Wealden, in Sussex, just below the chalk. Dr. Mantell was only a country practitioner, and when he first produced before the Geological Society his Iguanodon remains, and suggested that they were those of a reptile, some doubt was thrown on this conclusion, because geologists believed from the appearance of the teeth that the animal must be of some other animal family. But Dr. Mantell found that a little lizard living in South America had teeth like those he had discovered in his reptile remains, and he persisted in his view. Many years later a wonderful find was made near Brussels in a coal mine near Bernissart, the skeletons of no fewer than twenty-two huge Iguanodons were found complete and embedded in a fairly soft clay-like rock. The authorities of the Government Museum took charge of the place and most carefully removed the skeletons to Brussels, where the complete skeletons of seven were with enormous difficulty and care removed bit by bit from the rock and set up as entire skeletons in the Brussels Museum, where they may be seen. A replica of one of them is at South Kensington. The fore feet of the Iguanodon had five fingers, but the hind foot was very much like that of a bird, and had only three toes, and the bones of the pelvis or hip girdle were extraordinarily like those of a bird. When Professor Huxley examined the first fragments of the Iguanodon's remains he was inclined to believe them to be those of a gigantic bird; and it is generally believed now that it is from this extraordinary reptile stock that the birds were derived.

But the great lake with all its varied stores was doomed to sink lower and lower, till the great sea overwhelmed England. Another ocean joining it to the east overwhelmed Germany; and the whole of Europe, south of a line drawn through Scotland, Christiania, and Moscow, became sunk under salt water. There were patches standing up here and there—Ireland, Brittany, Cornwall, Spain or a good part of it, Switzerland, part of Italy (and also part of what is now the Western Mediterranean), and most of Turkey and Hungary. But elsewhere marine animals succeeded the reptiles, and the foundations of all the chalk hills and cliffs of modern Europe were laid.

Of what were they made? We may borrow a capital suggestion from Mr. Jerome Harrison, of Birmingham University. "Take," he says, "a piece of chalk and brush it vigorously with a tooth-brush in a glass of water until the liquid looks quite milky. Allow the greater part of the sediment to subside, and then pour away the water and wash the material which has sunk to the bottom of the glass by pouring water on it two or three times. Put the whitish powder which finally remains under a microscope; and examine it with, say, the quarter-inch power, which will magnify about 300 diameters. The greater part of the white powder will then be seen to be composed of the minute shells of creatures called Foraminifera—little specks of jelly-like matter which secrete for themselves a shell or covering from the carbonate of lime dissolved in the sea-water in which they live.

"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.

The heavy armour of the head of the Triceratops must have been developed for purposes of attack and defence, but we do not know whether it was for fighting their own species or for protection against the carnivorous reptiles. "So long," says Professor F. A. Lucas, "as Triceratops faced an adversary he must have been practically invulnerable, but, as he was the largest animal of his time, it is probable that his combats were mainly with those of his own kind, and the subject of dispute some fair female upon whom rival suitors had cast covetous eyes. What a sight it would have been to have seen two of these big brutes in mortal combat, as they charged upon each other with all the impetus to be derived from ten tons of infuriate flesh! We may picture to ourselves horn clashing upon horn, or glancing from each bony shield until some skilful stroke or unlucky slip placed one combatant at the mercy of his adversary....

"A pair of Triceratops's horns in the National Museum (at Washington) bears witness to such encounters, for one is broken midway between tip and base; and that it was broken during life is evident from the fact that the stump is healed and rounded over, while the size of the horns shows that their owner reached a ripe old age."

In connection with the concluding part of the last sentence it should be mentioned that reptiles, like fishes, but unlike birds and mammals, continue to grow throughout their entire span of life, so that unusually large bodily size is, at all events as a rule, an indication of advanced age. As regards general appearance Triceratops may, perhaps, be best described as a reptilian rhinoceros, with the proviso that the tail was much larger and thicker than in that group of animals, and passed insensibly into the body, as in reptiles generally, while the number and arrangement of the horns were different.

The Pterosaurs, or flying reptiles, made, as we have said elsewhere, a great advance. Williston regards them as having come to excel all other flying vertebrate animals. Some attained a wing-spread of twenty feet, and they could fly far and fast. They were all short-tailed; some of them probably could scarcely walk, and the larger of them had no teeth. Their bills resembled those of modern birds, and they have been styled the kingfishers of the Cretaceous seas. Terrific to look upon, they were probably not very deadly animals except to small fishes. The lizards did not make much progress; but the snakes made their first appearance, though they remained small; and the mammals showed little progress from the forms which were found in the previous era of the Jurassic.

At the close of the geological period whose natural physiognomy we have thus traced, Europe was still far from displaying the configuration which it now presents. A map of the period would represent the great basin of Paris (with the exception of a zone of Chalk), the whole of Switzerland, the greater part of Spain and Italy, the whole of Belgium, Holland, Prussia, Hungary, Wallachia, and Northern Russia as one vast sheet of water. A band of Jurassic rocks still connected France and England at Cherbourg—which disappeared at a later period, and caused the separation of the British Islands from what is now France.