the north.
59:4.11 Many of the largest true fish belong to this age, some of the teeth-bearing varieties being 7-9 m long; the present-day sharks are the survivors of these ancient fishes. The lung and armoured fishes reached their evolutionary apex, and before this epoch had ended, fishes had adapted to both fresh and salt waters.
59:4.12 Veritable bone beds of fish teeth and skeletons may be found in the deposits laid down toward the close of this period, and rich fossil beds are situated along the coast of California since many sheltered bays of the Pacific Ocean extended into the land of that region.
59:4.13 The earth was being rapidly overrun by the new orders of land vegetation. Heretofore few plants grew on land except about the water’s edge. Now, and
59:4.14 As the land rose, North America became connected with Europe by land bridges extending to Greenland. And today Greenland holds the remains of these early land plants beneath its mantle of ice.
59:4.15 ¶
59:4.16 ¶
59:4.17 ¶ The elevation of the continents proceeded, and the atmosphere was becoming enriched with oxygen. The earth was overspread by vast forests of ferns 30 m high and by the peculiar trees of those days, silent forests; not a sound was heard, not even the rustle of a leaf, for such trees had no leaves.
59:4.18 ¶ And thus drew to a close one of the longest periods of marine-life evolution,
5. THE CRUSTAL-SHIFTING STAGE
THE FERN-FOREST CARBONIFEROUS PERIOD
THE AGE OF FROGS
59:5.1 The appearance of fish during the preceding period marks the apex of marine-life evolution. From this point onward the evolution of land life becomes increasingly important. And this period opens with the stage almost ideally set for the appearance of the first land animals.
59:5.2 ¶
59:5.3 Shortly thereafter the central portion of North America was inundated, creating two great inland seas. Both the Atlantic and Pacific coastal highlands were situated just beyond the present shore lines. These two seas presently united, commingling their different forms of life, and the union of these marine fauna marked the beginning of the rapid and world-wide decline in marine life and the opening of the subsequent land-life period.
59:5.4 ¶
59:5.5 When the seas were at their height, a new evolutionary development
59:5.6 From the briny waters of the seas there crawled out upon the land snails, scorpions, and frogs. Today frogs still lay their eggs in water, and their young first exist as little fishes, tadpoles. This period could well be known as the
59:5.7 Very soon thereafter the insects first appeared and, together with spiders, scorpions, cockroaches, crickets, and locusts, soon overspread the continents of the world. Dragon flies measured 76 cm across. 1,000 species of cockroaches developed, and some grew to be 10 cm long.
59:5.8 Two groups of echinoderms became especially well developed, and they are in reality the guide fossils of this epoch. The large shell-feeding sharks were also highly evolved, and for more than 5,000,000 years they dominated the oceans. The climate was still mild and equable; the marine life was little changed. Fresh-water fish were developing and the trilobites were nearing extinction. Corals were scarce, and much of the limestone was being made by the crinoids. The finer building limestones were laid down during this epoch.
59:5.9 The waters of many of the inland seas were so heavily charged with lime and other minerals as greatly to interfere with the progress and development of many marine species. Eventually the seas cleared up as the result of an extensive stone deposit, in some places containing zinc and lead.
59:5.10 The deposits of this early Carboniferous age are from 150 to 600 m thick, consisting of sandstone, shale, and limestone. The oldest strata yield the fossils of both land and marine animals and plants, along with much gravel and basin sediments. Little workable coal is found in these older strata. These depositions throughout Europe are very similar to those laid down over North America.
59:5.11 Toward the close of this epoch the land of North America began to rise. There was a short interruption, and the sea returned to cover about half of its previous beds. This was a short inundation, and most of the land was soon well above water. South America was still connected with Europe by way of Africa.
59:5.12 This epoch witnessed the beginning of the Vosges, Black Forest, and Ural mountains. Stumps of other and older mountains are to be found all over Great Britain and Europe.
59:5.13 ¶
59:5.14 The land was periodically going up and down due to the shifting sea level occasioned by activities on the ocean bottoms. This crustal uneasiness — the settling and rising of the land — in connection with the prolific vegetation of the coastal swamps, contributed to the production of extensive coal deposits, which have caused this period to be known as the
59:5.15 The coal layers alternate with shale, stone, and conglomerate. These coal beds over central and eastern United States vary in thickness from 12 to 15 m. But many of these deposits were washed away during subsequent land elevations. In some parts of North America and Europe the coal-bearing strata are 5,500 m in thickness.
59:5.16 The presence of roots of trees as they grew in the clay underlying the present coal beds demonstrates that coal was formed exactly where it is now found. Coal is the water-preserved and pressure- modified remains of the rank vegetation growing in the bogs and on the swamp shores of this faraway age. Coal
