244 



GEOLOGY. 



Upper. From e to / the Upper Cambrian fauna is found. Between 

 / and g the faunal changes are again more rapid and more profound 

 than between b and c, or d and e. Since the changes at this horizon 

 are greater than at the other corresponding horizons below, the faunas 

 above and below fg are referred, not to different epochs of the same 



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Fig. 97. — Diagram to illustrate classification based on unequally rapid transitions of 

 faunas. The fossils of the strata, be, de, and fg record more rapid changes of life 

 than the strata ab, cd, and ef. be represents the transition from Lower Cambrian 

 to Middle Cambrian; de from the Middle Cambrian to the Upper Cambrian, and fg 

 from the Upper Cambrian to the Ordovician. ab, cd, and ef represent Lower, 

 Middle, and Upper Cambrian respectively. 



period, but to different periods. The beds between / and g therefore 

 represent the transition from the Upper Cambrian to the next succeed- 

 ing, or Ordovician fauna. 



A few years since, question was raised concerning the accuracy and sim- 

 plicity of the interpretation x of the Cambrian sketched above. One of the ques- 

 tions concerned the equivalence of the so-called Olenellus fauna of Newfoundland 

 and Europe, and those of the Hudson-Champlain valley and the western part 

 1 Matthew, Am. Geol.. Vol XIX, 1897, p. 395. 



