Vrof. T. Sterry Sunt — On Camhnan and Silurian. 563 



defended by Adams, at that time engaged in a Geological Survey of Vermont, 

 with which, in 1846 and 1847, the present writer was connected. [The subse- 

 quent palseoiitological discoveries are here discussed.] 



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, i860, satisfied 

 that "the fossils are of the age of the strata." la consequence of the discovery 

 of Mr. Billings, Logan now proposed to separate from the Hudson- River group 

 the Greywacke series of Bigsby and Bayfield, and ascribed to it a much greater 

 antiquity ; regarding it as "a great development of strata about the horizon of the 

 Chazy and Calciferous, brought to the surface 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 formation." This series, to 

 which was assigned a thickness of from 5000 to 7000 feet, he named the Quebec 

 group, which included 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. 



This important distinction once established, it was found necessary to draw a 

 line from the St. Lawrence, near Quebec, to the vicinity of Lake Champlain, 

 separating the true Hudson-River group, with its overlying Oneida or Medina 

 rocks, on the north-west side, from the so-called Quebec group, on the south and 

 east. 



As early as 1842, Prof. Hall, in a comparison of the Lower Palaeozoic rocks of 

 New York with those of Great Britain, declared the Potsdam to be lower than the 

 base of the Upper Cambrian or Bala group of Sedgwick. In 1847, as we have 

 seen, he extended this observation to the Calciferous and Chazy, both of which he 

 placed below this horizon ; which until a year or two previous had been looked 

 upon as the base of the Paleozoic series in Great Britain, and was subsequently 

 made the lower limit of the second fauna of Barrande. Although from these facts 

 it was probable that these lower members of the New York system might corre- 

 spond to the primordial fauna of Barrande, we still remained, in the language of 

 Prof. Hall, without " the means of parallelizing our formations with those 

 of Bohemia, by the fauna thei-e known. The nearest approach to the type of the 

 Primordial Trilobites was found in the Potsdam of the north-west, described by Dr. 

 D. D. Owen ; but none of these had been generically identified with Bohemian 

 forms, and the prevailing opinion, sanctioned, as I have understood, by M. 

 Barrande, was that the primordial fauna had not been discovered in this country 

 until the re-discovery (in 1856) oi Paradoxides Harlaiti at Braintree, Mass. [The 

 history of this Paradoxides is then related.] 



The geological examinations of Mr. Alexander Murray in Newfoundland since 

 1865 have shown that the south-eastern part of that island contains a great volume 

 of Cambrian rocks, estimated by him at about 6000 feet in all. No traces of the 

 Upper Cambrian or second fauna have been detected among these,_but some por- 

 tions contain the Paradoxides already mentioned, while others yield the fauna 

 which Mr. Billings has called Lower Potsdam. This name was first given in an 

 appendix (prepared by Sir W. E. Logan) to Mr. Murray's report on Newfoundland 

 for 1865, published in 1866 (page 46 ; see also Report of the Geol. Survey of 

 Canada for 1866, p. 236). The Lower Potsdam was there assigned a place above 

 the Paradoxides beds of the region, which were called the St. John group, — the 

 fossiliferous strata of St. John, New Brunswick, being referred to the same 

 horizon ; which corresponds to the Menevian of Wales, now recognized as the 

 summit of the Lower Cambrian. The succession of the rocks containing these 

 two faunas in south-eastern Newfoundland is not yet clear ; the Lower Potsdam 

 fauna is regarded by Mr. Billings as identical with that found on the strait of 

 Bellisle, at Bic (on the south shore of the river St. Lawrence, below Quebec), at 

 Georgia, Vermont, and at Troy, New York ; but in none of these other localities 

 is it as yet known to be accompanied by a Menevian fauna. The Trilobites hitherto 

 described iroin these rocks belong to the genera Olenclius, Conocoryphc, and 

 Agnosliis ; neither Paradoxides, which characterizes the Menevian and the under- 

 lying liarlfch Ijeds in Wales, nor Olenus, which there abounds in the rocks 

 immediately above this horizon, having as yet been described as occurring in the 



