4 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL.83 



grateful acknowledgment is hereby tendered. They include especially 

 Sir Arthur Keith, Sir A. Smith Woodward, and the gentlemen of 

 the Department of Geology and Palaeontology, British Museum 

 of Natural History. London ; Professors Arthur Thomson and 

 J. Dudley Buxton, of Oxford ; Professor R. R. Marett, of Cambridge, 

 England; M. Sinel, of the Museum of the Island of Jersey; Profes- 

 sors A. Rutot, Charles Fraipont and Maxime Lohest, with the sons of 

 the latter, and those in charge of the Musee du Cinquantinnaire, 

 in Brussels. Belgium ; Professor Marcellin Boule and Dr. Henri 

 Martin, Paris, with Professors Arcelin and Mayet, of Lyon, France; 

 the authorities of the Museums at Perigueux, at Toulouse, at Monte 

 Carlo, and at Barma Grande ; those of the National and Anthropologi- 

 cal Museums at ^Lidrid ; Professors Schwalbe, Lehner, Schoetensack, 

 G. Steinman and J. Sobotta, Preparator H. Lindig (Weimar), and 

 the authorities of the Museunts in Heidelberg, Bonn, Tubingen, 

 Stuttgart, Weimar, Jena, and Berlin, in Germany ; Professors J. 

 Matiegka, Karel Maska, and Karcl Absolon, in Prague, Tele, and 

 Brno, Czechoslovakia; I'mfessor K. Gorjanovic-Kramlierger. in 

 Zagreb; Professor Joseph vSzombathy, in Vienna; and many others 

 who cannot be mentioned here by name. 



The Glacial Period 



The Ice Age, or Pleistocene period of the Quaternary, was accord- 

 ing to all evidence the period most intimately associated with the early 

 history of man, possibly even witnessing his origin and determining 

 his development. It is the geological subdivision of time immediately 

 preceding the present, from which it is not sharply separated. The 

 present may be viewed in fact as still a part of the era of deglaciation, 

 for the ice has merely receded to the farther north and south and 

 higher up the mountains; vast parts of the earth are still perpetually 

 frozen or covered by glaciers. The only justifications for separating 

 the present as a period of its own lie in the seeming relative stabili- 

 zation of conditions, and in the general convenience of such a separa- 

 tion ; but there is no line of demarcation between the two, just as 

 doubtless there was none between the Glacial Age and that which 

 preceded it. 



To facilitate jjroper orientation it may be useful to show here the 

 conventional geologic subdivision of the earth's history, though it is 

 lintb very imiK-rfect and largely artificial. The accompanying chart 

 has been i)rcix'ired by Dr. R. S. I'.assler. Head Curator of the Depart- 

 ment of Geology, U. S. National Museum, who has kindly permitted 

 use of it. 



