106 A CENTURY OF SCIENCE 



than early Paleozoic. Other undated Proterozoic tillites 

 occur in China (Willis and Blackwelder 1907), Africa 

 (Schwarz 1906), India (Vredenburg 1907), Canada 

 (Coleman 1908), and possibly in Scotland. 



The oldest known tillites are described by Coleman in 

 1907, and occur at the base of the Lower Huronian or in 

 early Proterozoic time. They extend across northern 

 Ontario for 1000 miles, and from the north shore of Lake 

 Huron northward for 750 miles. 



Fossils as Climatic Indexes. Paleontologists have 

 long been aware that variations in the climates of the 

 past are indicated by the fossils, and Neumayr in 1883 

 brought the evidence together in his study of climatic 

 zones mentioned elsewhere. Plants, and corals, cepha- 

 lopods, and foraminifers among marine animals, have 

 long been recognized as particularly good "life ther- 

 mometers." In fact, all fossils are climatic indicators 

 to some extent, and a good deal of evidence concerning 

 paleometeorology has been discerned in them. This evi- 

 dence is briefly stated in the paper by Schuchert already 

 alluded to, and in W. D. Matthew's Climate and Evolu- 

 tion, 1915. 



Sediments as Climatic Indexes. Johannes Walther in 

 the third part of his Einleitung Lithogenesis der 

 Gegenwart, 1894 is the first one to decidedly direct 

 attention to the fact that the sediments also have within 

 themselves a climatic record. In America Joseph Bar- 

 rell has since 1907 written much on the same subject. 

 On the other hand, the periodic floodings of the con- 

 tinents by the oceans, and the making of mountains, 

 due to the periodic shrinkage of the earth, as expressed 

 in T. C. Chamberlin's principle of diastrophism and in 

 his publications since 1897, are other criteria for estimat- 

 ing the climates of the past. 



Conclusions. In summation of this subject Schuchert 

 says: 



"The marine 'life thermometer' indicates vast stretches of 

 time of mild to warm and equable temperatures, with but slight 

 zonal differences between the equator and the poles. The great 

 bulk of marine fossils are those of the shallow seas, and the evo- 

 lutionary changes recorded in these 'medals of creation' are 

 slight throughout vast lengths of time that are punctuated by 



