360 PRE-CAMBRIAN PERIODS 



these regions are found rocks like the typical Archaean, which 

 stand in the same relation to the newer groups, but how much 

 should be referred to these newer groups is still a question. 



In the other continents occur great areas of very ancient gneisses 

 and crystalline schists, but even less than in North America has the 

 distinction been made between the fundamental complex and newer 

 groups. In the following statements no attempt is made to deter- 

 mine how much of the areas mentioned is properly Archaean. 



In Europe the principal area lies to the north, covering parts of 

 Ireland and the Highlands of Scotland, with which was probably 

 once connected the great continuous mass of Scandinavia, Fin- 

 land, and Lapland. Considerable areas also occur in central 

 and southern Europe, as the central plateau of France, parts of 

 Germany and Bohemia, and long, narrow belts in the Pyrenees, 

 Alps, and Balkans. In Asia these ancient crystalline rocks are 

 found in the great mountain ranges, such as the Himalayas, Altai, 

 etc. They make up a large part of the Indian peninsula, and are 

 extensively displayed in China, Japan, and the islands of the Malay 

 Archipelago. The vast central plateau which occupies so much 

 of Africa is principally composed of these rocks, which are also 

 largely exposed in Australia. In South America similar rocks 

 appear in the highlands of Brazil and in the Andes. 



Origin of the Archaean Rocks. — This is a problem which has 

 given rise to a great deal of discussion and is still far from solu- 

 tion. One reason for the great differences of opinion is the 

 varying extension which has been given to the term Archtzan, 

 one writer including rocks which another excludes. The principal 

 suggestions which have been offered are the following : — 



(1) That the Archaean rocks are entirely of igneous origin and 

 represent part of the original crust of the earth, added to from 

 below by solidification and cut by many subsequent igneous intru- 

 sions. On this view these rocks are far older than any sediment- 

 aries whatever. 



(2) That the Archaean rocks were precipitated from solution 

 in the hot seas which first condensed, under great atmospheric 

 pressures, upon the highly heated crust. 



