IjAWSON.] 



The Eparchcedn Interval. 



were first clearly appreciated by James D. Dana, and in 1872 he 

 proposed Archaean as a general term including the Laurentian, 

 Huronian and other pre-Cambrian rock series which might or 

 might not be the correlatives of these. The term Azoic had 

 earlier been used for the non-fossiliferous, pre-Silurian rocks, 

 but the use of the name implied the adoption of a very ques- 

 tionable theory, and it fell into disuse very rapidly after Dana's 

 suggestion. Few terms in geology have met with wider or more 

 rapid acceptance than Dana's Archman. It has become firmly 

 established in the literature of many languages, and particularly 

 in the literature of North American geology. 



The rocks of Archaean age, as it is universally understood, 

 undoubtedly comprise a vast quantity of igneous rocks which 

 were at one time supposed to be metamorphic sediments, but it 

 also comprises the unquestionably clastic Grrenville and Huronian 

 series. 



These facts were as well known in 1889 as they are to-day, 

 yet in that year a remarkable proposal was made for the over- 

 throw of the term Archaean as a designation embracing pre- 

 Cambrian clastic rocks. A conference of the geologists of the 

 United States Geological Survey in that year, considering the 

 nomenclature to be used in the publications of the Survey,* 

 agreed: That the term Algonkian be used as the designation of 

 the time of deposition of clastic rocks older than the Cambrian; 

 and further that the oldest time division shall cover the time of 

 formation of the ancient crystalline rocks and its designation 

 shall be the Archman. This is virtually a substitution of the 

 term Algonkian for Archaean in stratigraphy, in spite of the well 

 established use of the latter term, which cannot be maintained 

 except in direct violence of the law of priority and by an official 

 fiat which is generally recognized as without force in scientific 

 matters. The term Archaean already covered the pre-Cambrian 

 elastics known as the Grenville and Huronian series. 



The term Algonkian being inadmissable by the law of prior- 

 ity for the clastic rocks of the Archa?an, it remains to inquire 

 whether there be any justification for the use of the term. Clearly, 



*U. S. G. S., Tenth Ann. Rpt., Pt. I. 



