DISCRIMINATION OR TIME-VALUES IN GEOLOGY 585 



divisions of the scale, as furnisliing a convenient set of diag- 

 nostic species ; they, too, do not in every case avoid lapping, a 

 difificulty which it has already been said is unavoidable when the 

 means of measurement are multiple and not mutually exclusive. 

 The foregoing table is offered, then, as a means of illustrating 

 the proposed plan. 



Henry Shaler Williams. 



New Haven, Conn. 



