[ells] CANADIAN GEOLOGICAL NOMENCLATURE 17 



As for the crystalline rocks, such as the granites, gneisses, schists and 

 quartzites, with their associated limestones, the old terra Primitive stiJî 

 continued to designate this great series. This term, in 1843, gave 

 place to the term Gneissoid and Metamorphic group, the latter being 

 introduced by Murray in that year for the rocks of this series ; and these 

 names were continued in use for the crystalline rocks down to 1853-53. 



In the Keport of the G-eological Survey for that year, Logan, 

 recognizing the difficulty of placing such an enormous thickness of rocks, 

 which formed the great series below the fossiliferous sediments, under 

 such a comprehensive title, made use of the term Laurentian, which Avas 

 designed to include the lower portion of the series, giving as his reason 

 for so doing " that inasmuch as this term Metamorphic was applicable to 

 any series of rocks in an altered condition, and might occasion confusion, 

 it has been considered expedient to apply to these for the future, the more 

 distinctive appellation of the Laurentian series, a name founded on that 

 given by Mr. Garneau to the chain of hills which they compose." 



The introduction of this term Laurentian in Canadi'an nomenclature 

 marks the advent of a new era in the study of the crystallines and the 

 overlying rocks of the St. Lawrence basin. From the enormous develop- 

 ment of the former in central and eastern Canada, the opportunities for 

 their study on the large scale are probably much greater than in any 

 other known geological field; and since the early date when Logan ap- 

 plied his historic name to the oldest of our rock formations, the study 

 of their structure and relations has been steadily followed up. Of these 

 old rocks it may be said that their investigation has furnished most in- 

 teresting and complex problems, which have engrossed the attention, 

 not only of Canadian geologists, but of those in England and the United 

 States as well. 



In a small volume, published in connection with the Paris Exhi- 

 bition of 1855, styled '^ Esquisse Géologique," the new term Huronian 

 was first applied by BLunt to a portion of these rocks which had been 

 particularly studied in the vicinity of Lake Huron, This name was re- 

 garded as partly synonymous with the lower Cambrian of Sedgwick, and 

 it was held to include a considerable part of what in Bigsby's paper of 

 1820, on this area, was classed as the Transition group. The Huronian 

 rocks of that day comprised a very considerable thickness of schists, 

 quartzites, conglomerates, slates, etc., which were regarded generally as 

 unconformable to the underlying gneiss and granite which had so recent- 

 ly been styled Laurentian. Regarding the earlier views as to the age 

 of these rocks, Sedgwick had, some years previous to the introduction of 

 the term Huronian, stated that they belonged to a horizon below the 

 lowest recognized Cambrian of Wales, and this view was later maintained 



Sec. IV., ISO!). 2 



