XV.] CAMBRIAN AND SILURIAN IN NORTH AMERICA. 401 



be assigned a position in the first or primordial fauna. This 

 conclusion he communicated to Mr. Barrande in a letter dated 

 July 12, 1860 (American Journal of Science (2), XXXI. 220), 

 and gave descriptions of many of the organic forms in the 

 Canadian Naturalist for the same year. I have already alluded, 

 in describing the rocks of Point Levis, to the peculiarities of 

 aspect which probably led Dr. Bigsby, in 1827, to confound 

 these fossiliferous limestones penetrated by dolomite, with the 

 true dolomitic conglomerates associated with them, and helped 

 him to suppose the fossils to be derived from the limestones of 

 the north shore, now known to be younger rocks. This mis- 

 take was a very natural one at a time when comparative pale- 

 ontology was unknown. 



Sir William Logan meanwhile made a careful stratigraphical 

 examination of the rocks of Point Levis, and, notwithstanding 

 the peculiarities of the limestones which there contain the 

 primordial fauna, declared himself, in December, 1860, satisfied 

 that " the fossils are of the age of the strata." In consequence 

 of the discovery of Mr. Billings, Logan now proposed to sepa- 

 rate from the Hudson Eiver group the graywacke series of 

 Bigsby and Bayfield, and ascribed to it a much greater an- 

 tiquity ; regarding it as " a great development of strata about 

 the horizon of the Chazy and Calciferous, brought to the sur- 

 face by an overturn anticlinal fold, with a crack and a great 

 dislocation running along the summit," by which the rocks in 

 question were "brought to overlap the Hudson River forma- 

 tion." This series, to which was assigned a thickness of from 

 5,000 to 7,000 feet, he named the Quebec group, which in- 

 cluded the green sandstones of Sillery, regarded as the summit, 

 the fossiliferous limestones and graptolitic shales at the base, 

 which afterwards received the name of the Levis formation, 

 and a great intermediate mass of barren shales and sandstones, 

 called the Lauzon formation. The first account of this change 

 in the stratigraphical views of Logan occurs in his letter to 

 Barrande, dated December 31, 1860. (American Journal of 

 Science (2), XXXI. 216.) 



This important distinction once established, it was found 



z 



