PRE-CAMBRIAN CLASSIFICATION IN ONTARIO 587 



was taken away and the name Laurentian came to stand only for 

 granite and gneiss of undoubted igneous origin, older than the 

 so-called Huronian sediments.^ 



CLASSIFICATIONS NOW IN USE 



The need for a revision of the classification and nomenclature 

 of the pre-Cambrian rocks has been felt from time to time as 

 knowledge concerning them has increased. 



Table I shows the classification that has been adopted by the 

 authors.^ Like all other classifications it will be subject to revision 

 when a more perfect understanding of the relations of the rocks 

 is acquired. 



In Table II are given the classifications employed by several 

 other authors. 



LAURENTIAN AND HURONIAN 



Logan, himself, when introducing the names Laurentian and 

 Huronian said: "These local names are, of course, only provisional, 

 devised for the purpose of avoiding paraphrastic or descriptive 

 titles, the use of which had been found inconvenient, and they can 

 be changed when more important developments, proved to be the 

 equivalents of the series, are met with elsewhere."^ Hence, when 

 it is found advisable to change the classification or to discard the 

 now historic names, looked on by Logan as being only provisional, 

 mere sentiment should not be permitted to stand in the way. In 

 most cases it is better to discard a name rather than employ it in 

 a new sense. 



As shown in a preceding paragraph, the term Laurentian is 

 now used in a much-restricted sense and, as will be seen from the 

 following pages, different meanings are attached to it by various 

 authors. The earlier literature in which Laurentian rocks were 

 described has become almost unintelligible. 



Much confusion has arisen also through the employment of 

 the classic name Huronian, especially with the prefixes Upper, 

 Middle, and Lower, in different senses. The term Lower Huron- 

 ian, for example, has been applied indiscriminately to certain rocks 



' Report of International Committee, Jour. Geol., February-March, 1905. 



2 Ont. Bur. Mines, XXII, Part II, Appendix. 



5 American Association for the Advancement of Science , 1857. 



