CHAPTER XIX 



THE QUATERNARY PERIOD 



By the very nature of the case, our usual method of discussion 

 cannot be applied to the Quaternary period without considerable 

 modification, the characteristic feature having been vast sheets 

 of ice covering much of the northern hemisphere. Otherwise the 

 earth had reached essentially its present geological condition. 



Origin of Name, Subdivisions, etc. 



As pointed out toward the beginning of the last chapter, the 

 terms " Tertiary" and ''Quaternary" are both remnants of an old 

 geological nomenclature, and both have entirely lost their original 

 significance. The Quaternary is the last great period of earth 

 history, the study of which leads us right up to present-day geo- 

 graphic and geologic conditions. During this period nearly all of 

 the existing species of invertebrates and lower Vertebrates, as well 

 as most of the existing species of Mammals, had appeared. Except 

 in the glaciated regions, the line of separation between the Tertiary 

 and the Quaternary is not at all clearly defined. 



Following the usual method, we shall divide the Quaternary 

 period into (1) • the Pleistocene or Glacial epoch, which represents 

 the time of ice occupation of northern North America and northern 

 Europe, and (2) the Recent or post-Glacial epoch or time since the 

 removal of the ice from those continents. We are living in the 

 Recent epoch. 



The Fact of the Ice Age 



The Quaternary period was ushered in by the spreading of vast 

 ice sheets over much of northern North America and northern 

 Europe. This event must take rank as one of the most interesting 

 and remarkable occurrences in geological time. On first thought, 

 the existence of such vast ice sheets seems unbelievable, but the 

 Ice age occurred so short a time ago that the records of the event 

 are perfectly clear and conclusive. The fact of this great Ice age 

 was discovered by Louis Agassiz in 1837, and fully announced 



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