48 FORMATION OF THE EARTH 



the presence in this area of a high mountain chain during the 

 Devonian epoch. These mountains, after a period of 

 quiescence, seem to have extended to other parts of South 

 Africa, India, and Australia. At any rate, during the second 

 half of the Carboniferous Period in which the coal deposits 

 were formed, enormous glaciers, uniting at certain points, 

 developed on the slopes of the high mountains in the southern 

 portion of the huge continent of Gondwana, which then com- 

 prised Brazil, Africa, Madagascar, India, New Guinea, and 

 the western portion of Australia, and whose southern coast 

 was washed by the southern ocean. 



It was also at this time that the Hercynian chain arose on 

 the North Atlantic continent, which was then washed by the 

 tropical Tethys or Central Mediterranean Sea. Both in the 

 North Atlantic and the Gondwana continents the land 

 vegetation assumed, during the first part of the Carboniferous 

 epoch, an importance it had not hitherto possessed. The 

 uprising of the Hercynian range and the volcanic eruptions 

 accompanying it troubled the ocean waters. The corals 

 abandoned these shores and retired to the north, to the region 

 of Dinant in Belgium, the Pennine chain in England, and even 

 the neighbourhood of the Pole. The temperature of the sea 

 in this area, therefore, did not fall below 20°, the temperature 

 essential for the development of coral reefs to-day. The 

 Hercynian chain soon attained its greatest altitude ; its slopes 

 became covered with a rapidly growing vegetation of the non- 

 flowering plant families, whose only representatives to-day are 

 modest herbaceous plants, such as club-moss, the selaginaceae, 

 and horse-tails, or those whose flowers are still in an 

 undeveloped stage, such as conifers. The torrents rushing down 

 these mountain slopes became powerful streams, which 

 uprooted trees and carried them to lakes and wide estuaries 

 where they collected and helped to form coalfields such as 

 those in the south of England, the north of France, and 

 Belgium. At the foot of these slopes, in vast marshes, there 

 grew also plants with long underground stems, ferns, and 

 cycads, whose leaves, dead branches, and trunks then 

 accumulated where they were and led to the formation of coal- 

 fields of another type, such as those of the Central Plateau, 

 for instance. The richness of these deposits is such that it was 

 at one time believed, owing to an illusion comparable to that 



