April 1, 1886.] 



♦ KNOW^LEDGE ♦ 



173 



It should be noted that if any approach to the exception- 

 ally hot and humid climate, generally supposed to prevail 

 during the carboniferous period, actually did exist, the 

 luxuriance of vegetation on the slopes of the fjords of that 

 period must have been vastly greater than those of Norway, 

 and the rate and quantity of vegetable deposition propor- 

 tionally magnified. 



I have yet to consider the peculiarities of the strata 

 above and below the actual seams of coal ; will describe 

 them and discuss their formation in my next. 



THE STORY OF CREATION. 



a i'laix acrount of evolution. 



By Edwarh Clodd. 



VI.— THE PAST LIFE-HISTOEY OF THE EARTH (^Conduded). 





HE warm climates of tlie Secondary epoch 

 prevailed far into the Tertiary, but were 

 followed by declining temperatures, which 

 at last resulted in the long and intermit- 

 tent period of intense cold known as the 

 Glacial epoch, when large areas of Europe 

 and North America were swathed in ice. 

 which gouged and moulded the subsiding land, clioking the 

 sea w-ith debris, and destroying numberless species of plants 

 and animals, to the lasting biological impoverishment of 

 after times. In the end the temjierature rose to its present 

 level. 



The Tertiarj' epoch marks the beginning of the present 

 order of things, of the distribution of land and se;x, and the 

 uprising of most of the great mountain chains. Although 

 much of the existing land area was then submerged under 

 shallow seas, the continents of both hemispheres had well- 

 nigh the same outlines as now. Varied as are the life-forms 

 of that epoch, unrelated and, save in the nummulitic lime- 

 stones, detached as are the strata, those life-forms manifest 

 a gi-adual approach to existing species, and a marked diver- 

 gence from the species of older epochs. The colossal reptiles 

 of Juras.sic and Cretaceous times, the coiled ammonites and 

 other mollusca of their seas, are extinct. The Age of huge 

 Reptiles has given place to the Age of huge Mammals, with 

 its intermediate forms, but with no one species dominant, 

 and with no impoi'tant species imrepresented. 



The links between the Secondary and the Tertiary epochs 

 are, with rare exception, only meagrely represented liy any 

 known strata, for denudation has wellnigh swept awav the 

 intermediate deposits with their contents. And so confused 

 are the Tertiary strata that their order in time is determined 

 solely by the proportion of their shell-fish to existing species, 

 ranging from as low as three per cent, in the oldest lieds to 

 ninety-five per cent, in the newest. Mollusca have been 

 called the alphabet of paleontology, because their extensive 

 distribution through the .several epochs renders tliem the 

 most valuable and trustworthy of all organic remains in 

 assigning the order in time, and the conditions of life, not 

 only of their own species, but of other species whose life- 

 history is briefer, and whose range is more limited. 



The rocks of the Tertiai-y epoch witness to wide-spread 

 .aqueous and volcanic action. This is specially noticeable in 

 the Eocene strata, prominent among which are the vast 

 beds of limestone laid down when Europe, its north-west 

 corner excepted, and t'entral Asia were covered by the sea. 

 and which extend from the Pyrenees to China and Japan, 

 and also largely compose the Alps, Carpathians, Himalayas, 

 Atlas, and lesser mountain-chains. Not many nol)]e nor 

 mighty are called to the enduring tasks of nature. It is 



the minute .agents, unresting and wide-spread, that have been 

 the efficient causes of much that is grandest in earth-struc- 

 ture, and it is of shells of the coin-like nummulites that 

 these stupendous formations are mainly composed. Their 

 foundations were laid in Archajan times in the deep, broad 

 fissures opened in the crust by volcanic action. Into tliese 

 fell the sediment and org.anic deposits of ancient .seas, which 

 ultimately, as the cooling crust caved-in by its own weight 

 upon the shrinking hot nucleus, were squeezed and puckered 

 and overturned by lateral pressure into numberless folds. 

 Then, when the twisted and crumpled strata were upheaved 

 above sea le vel, water and the powersoftheair sculptured them 

 into pinnacle and peak, into ravine and valle\'. So the big 

 mountains, as we know them, are relativelj" modern ; the 

 lesser ones ai'e the older, a.s longest subject to the wear and 

 tear of eroding agents. Jlont Blanc and the Matterliorn 

 are not older than the Eocene marine clay on which London 

 stands, and the Rigi, a freshwater shingle-bed, is younger 

 still. 



Broadly grouping the life of Eocene seas, we find large 

 whales, teleostor bony-skeletoned fish in abundance, and the 

 persistent ganoids. Birds are in the air ; crocodiles and 

 tm-tlos swarm in the shallows ; * snakes and serpents make 

 their first appearance ; the mammals are no longer I'estricted 

 to pouch-bearei-s, for the placentals have invaded Europe in 

 large numbers — huge quadrupeds, carnivora, hornless deer, 

 and hog- like forms of a type between the tapir and the horse. 

 Among the most remarkable fossils from North American 

 beds are those of the ancestor of the horse, a creature about 

 the .size of a fox, with four hoofed toes on each foot, and in 

 one form {Eohippus) with the rudiments of a fifth toe, of the 

 importance of which more anon. A still more significant 

 biological link is found in the lemuroids of the Upper 

 Eocene (whicli belong to the Primates, or order of mammals 

 including man and ape), possessing characters allying them 

 to one or other of the hoofed quadrupeds then living. The 

 plants, which were slowly dispensed over the Northern hemi- 

 sphere from Polar regions, were tropical in character, as 

 sho-(vn by remains in the Thames delta and corresponding 

 deposits. 



The like applies to the flora of early Miocene (in which is 

 included 01igoceni>) times, when timber-trees, evergreens, 

 and water-lilies flourished within eight degrees of the North 

 Pole, with which Europe and America were connected by 

 way of Iceland and Greenland, although, such are the 

 puzzling climatal variations of past epochs, icebergs were 

 then floating in Northern Italy. The animals approximate 

 more nearly to those of the present, save in the huge size of 

 the mammals, as the m;\stodon and other creatures allied to 

 the elephant ; monkeys as large as a man appeared ; the 

 horse corresponded more nearly to his modern descendant, 

 the variation being that each foot had three toes, of which 

 only one touched the ground. Birds and insects were 

 abundant : of the latter 1,300 species have been found in 

 Switzerland alone. 



The Pliocene period ushered-in great local changes in land 

 and water distribution. The lofty ridge, clothed with oaks 

 and vines, that had stretched from France to Greenland, 

 and the remnants of whose lofty volcanic chain, of which 

 Hecla is the sole active relic, ai-e extant in the Hebrides 

 and the highlands of Scotland and Wales, was submerged. 

 Europe was thus severed from America, but Britain 

 was left as a peninsula, the newly-invading waters of the 

 North Sea dividing Scotland from Norw.ay. On the other 

 hand, the Eurasian contment was upraised in parts, leaving 

 the deeper basins of the Black, the Aral, and the Caspian 



* " More true turtles have left their remains in the London 

 clay at the mouth of the Thames than are known to exist in the 

 whole world."— Sir R. Owen, " Paleontology," p. 281. 



