Revieics — Wldtnet/ and Wadsicorth' s Azoic System. 31 



of the unknown. If this "fact" be admitted, of course there is an 

 end of the matter. If time can be kept onlj'^ by a gold watch, it is 

 useless to purchase a silver one. But some of us can remember 

 that, long before Archgean geology became a prominent study, 

 attempts were made to keep geological time without the aid of 

 fossils. The Harlech grits and the Tarannon shales, for example, 

 were assigned their approximate place without a particle of fossil 

 evidence ; and, even if the past conclusions of Arch^an geologists 

 should prove to be altogether fallacious, it seems scarcely scientific 

 to assume that only one test of age is applicable, and on this ground 

 to prohibit efforts to make out a succession in the Pre-Cambrian 

 rocks. 



Our authors state (p. 560) that " only lithological principles are 

 used in making these (Dr. Hunt's) divisions, and eveiy fact pertaining 

 to the origin and relations of these rocks is ignored." If this is so, 

 Dr. Hunt must be very wild indeed. But having thrice read his 

 •'Trap Dykes and Azoic Eocks " with great care, the present reviewer 

 must in justice affirm that a large proportion of that elaboi'ate work 

 is occupied in attempts (successful or otherwise) to explain " the 

 origin and relations " of the rocks in question. The "contribution " 

 Avhich our authors offer under this head is, of course, that " litho- 

 logical principles " should not be exclusively employed, a piece of 

 advice which will be unanimously, if not thankfully, accepted. 



This paper will fitly close with our authors' last " contribution " 

 to a settlement. Side by side with Dr. Hunt's " Chronological 

 arrangement of the Crystalline Rocks," based, they say, exclusively 

 upon " lithological principles," is presented a new classification of 

 their own, constructed upon the same model. It is as follows : — 



Laurentian Granites, Gneisses, and Syenites. 



SiDERiAN Magnetite, Hematite, Menaccanite. 



Ophian Peridotites, including Serpentines. 



JSToKiAN Gabbros, coarse Diabases and Diorites. 



Arvonian Felsite, Quartz Porphyry, Petrosilex, Jaspilite. 



PoRPHYKiAN Porphyrites. 



HuRONiAN Diorites, Diabases, Melaphyres, Chlorite Schists. 



MoNTALBAN- Mica schists. 



Crystallian Quartzites, Quartz schists. 



Taconian Limestones. 



Glacian Conglomerates. 



Pelodian Argillites. 



It is, of course, impossible to exhaustively criticize this book 

 within the limits of a short paper. All that has been attempted is 

 to emphasize some wise cautions which Archeean geologists have 

 sometimes neglected ; to point out wherein the authors have mis- 

 stated or misunderstood the views of their opponents, and to show 

 that their own contributions towards a settlement add little or 

 nothing to the controversy. 



In conclusion, it may be suggested that wholesale charges of 

 ignorance and incompetence are not arguments, and do not tend to 

 mitigate controversial acerbity. C. Callaway. 



