xvi TABLE OF CONl'ENTS. 



of the Archfean rocks are fossiliferous, and states what the life of that epoch 

 must have probably been, 548 ; his "abundance of life," however, only a theo- 

 retical abundance, 548. All eruptive and crystalline rocks, except the meta- 

 morphic Palaeozoic and post-Palieozoic, according to Dana, "Archtean," 548, 

 549 ; unphilosophical character of this idea, 549, 550. 



Inquiry into the propriety of the division of the Azoic (Archajan) into two or more 

 groups, 550-560 ; according to Dana's views, this absolutely necessary, 550. 

 The attempts of the Canada Survey to do this on the evidence of fossils, 551, 552; 

 the Aspidella and Arenicolitcs, 551, 552. Geological time kept by the order of 

 succession of life, and not by means of minerals, 552 ; the Canada Survey, and 

 the results of its attempts to follow the latter method, 552. 



How such methods came to be in vogue, 552. By what principles the Canadian 

 Survey Was governed, 553. Logan the author of them, 553 ; with what train- 

 ing he began it, 553, 554 ; his age at the time he published his first scientific 

 paper, 554 ; the influences under which he worked, 554 ; he follows Lyell 

 implicitly, 555 ; he begins the work with certain theoretical assumptions, the 

 truth of which he never investigates, 555 ; how his erroneous interpretation of 

 the geology of Lake Huron and Lake Superior led him to false conclusions, 556. 

 The Report of 1863 assumed certain things as having been proved which had 

 not been, 556. Hunt's statements about his own or other people's work not to 

 be accepted as authority until his quotations have been compared with the 

 original authorities, 556. The question of the nonconformity of the Laurentian 

 and Huronian looked into, 556 ; what ought to be seen if the two are uncon- 

 fomiable, and what is seen, 556, 557 ; Selwyn's statements on this point, 557. 

 What takes place when eruptive rocks begin to be acted on by erosive agencies, 

 557. What basis of fact underlies the division of the Azoic roi:ks into two 

 series, 558, 559. Logan takes the ground that lithological characters are suffi- 

 cient for the arrangement of rocks in chronological order, 559 ; in accordance 

 with this view, the rocks previously called Huronian still farther differentiated, 

 560 ; the gabbros thus separated, 560 ; the Hastings series, demonstrated by 

 Vennor to be continuous with the Laurentian, made into the Montalban and 

 Taconian, 560 ; the Arvonian, 560. Tabular arrangement of the rocks as at 

 present adopted by the Canada Survey, 561; some improvements, and a carrying 

 farther forward of the same idea, suggested in another table, 562 ; comments 

 on this mode of work, 562. Importance to American geologists of having the 

 work of the Canada Survey done according to better methods, 562. 



Appendix : Examination of some of Irving's statements, made in the Third Annual 

 Report of the United States Geological Survey, 563-565. 



