GEOCHRONOLOGY DE GEER 693 



mains of plants and animals, which more or less differ from any ex- 

 isting species. Naturally enough these earlier layers formerly 

 attracted the most attention, and the Quaternary deposits were looked 

 on mainly as a hindrance to the study of the older formations. 

 Geologically speaking, the Quaternary period was a very short one, 

 and the corresponding geological deposits are, in many places, incon- 

 siderable and uninstructive. Moreover, they vary considerably from 

 one region to another, both in thickness and material, and no general 

 classification of subdivisions has hitherto been possible. Now, how- 

 ever, there are special opportunities of gradually establishing a real 

 time scale for the Quaternary period. 



It would seem that the remarkable deterioration of the climate, 

 which caused the glaciation of the Quaternary period and can now 

 be shown to have affected the whole of the earth simultaneously, 

 must have had a great influence upon the ancestral forms of man, and 

 especially so in the regions where it was most severe. This influence 

 may indeed have been the immediate cause of that adaptation to more 

 and more exigent natural conditions and the consequent evolution 

 of intelligence which led to the beginning of the human stage. This 

 was especially true of regions where the supply of edible fruits 

 became insufficient and fishing and hunting became necessary. This 

 led to the development of skill and weapons, while the rigors of 

 climate necessitated the use of clothing and sheltered dwellings. 

 One invention led to another, such as the making of boats, the art 

 of pottery, and that important step in human evolution when man 

 took fire into his service. By extensive excavations in many regions 

 archeology has now been able to establish the succession in which 

 the various types of tools and weapons follow each other, and also 

 which species of animals and plants have been observed together with 

 these finds. In this way, for certain regions, it has been possible 

 to establish so regular a succession of strata as may well justify at- 

 tempts at correlation within limited areas. With regard to finds 

 from more widely separated regions, however, the risk of error is 

 naturally growing. Primitive types of tools, for instance, are known 

 to have originated independently in different places and epochs and 

 may likewise have been used for varying lengths of time in different 

 regions. Thus, to take a well-known example, certain tribes have 

 existed up to the present day with no knowledge of metals, and are 

 still to all intents living in a kind of Stone Age. 



Attempts have often been made to establish the sequence of those 

 climatic changes which seem to be indicated by the organic remains 

 found in various archeological strata. At many places, however, the 

 sequence of strata is very incomplete and, as the Quaternary period 

 shows several considerable climatic variations, it is often difficult to 



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