RARITY OF POST-ARCH^AN LIMESTONES. 87 



among the Archaean rocks, that the hemithrenes and ophites 

 constituting this series were only in process of elaboration when 

 the Lower Cambrians were in course of formation. 



It would be of importance to learn if any specimens of hemi^ 

 threne or ophite occur in the Archaean conglomerate of the 

 Coulonge river and other places. The circumstance would have 

 to be accepted as proving that the methylosis which had de- 

 veloped the crystalline limestones had set in antecedent to the 

 formation of the conglomerate. 



The explanation involved in the above suggestion embraces all 

 the facts of a problem which is unresolvable by either of the 

 doctrines we are opposed to, as regards the origin of the Archaean 

 hemithrenes and ophites; for if one were true, its advocates 

 would be able to point to something less vulnerable than 

 sparingly-developed limestones of the Cambrians ; or if the 

 other were a fact, its supporters would be able to refer to other 

 than the little better than corneous fossils characteristic of the 

 same rocks. Again, why chemical calcareous precipitates should 

 cease, or why the presumed " Eozoon Canadense " should precede 

 others only furnished with skeletons of a larval type, while it 

 never puts in an appearance subsequent to the Archaean periods, 

 except in the like methylosed and crystalline rocks, as the ophites 

 or hemithrenes of Connemara, Ceylon, Aker, Mt. St.-Philippe, 

 the Isle of Skye, and other places (most of them considered to 

 be Postarchaean, the last-named one being Jurassic), are also 

 questions which require to be satisfactorily answered. 



In the meantime we must continue to put faith in our sug- 

 gestion that the rarity of limestones in the Lower Cambrian 

 system is due to the absence of preexisting calcareous rocks from 

 which they could be derived that the great series of Archaean 

 crystalline limestones, which would represent such preexisting 

 rocks, was only imperfectly elaborated during the Lower 

 Cambrian period. This we beg to be accepted as our answer to 

 the question, Why are limestones comparatively rare in the 

 formations immediately succeeding the Archaeans ? 



The preceding observations, we wish it to be understood, refer 

 to Cambrian calcareous deposits that have undergone neither 

 mineral nor chemical changes : we are thus particular because it is 

 well known there are certain metamorphosed groups which com- 

 prise crystalline limestones and ophites, in Canada, the State of 



